Miocene and Pliocene Pectinidae (Bivalvia) from the Lee Creek Mine and Adjacent Areas Thomas G. Gibson possible, with the currently used stages of Europe and ABSTRACT radiometric time scales by means of correlations based on planktoni cForaminifera. Seventeen taxa of Pectinidae (Bivalvia) from lower Mio¬ Detailed quantitative morphologic studies were made on cene to lower Pleistocene strata in the Lee Creek Mine, 17 taxa, employing large population samples of most spe¬ North Carolina, and surrounding region were studied bio- cies. These studies allowed the establishment of morpho¬ metrically. The study of large population samples clarifies logic characters that both characterize the taxa and allow the relationships of the taxa and their biostratigraphic util¬ their differentiation. The characters found to be of most ity. Because of widespread geographic distribution of the species into various environmental conditions and relatively importance are those of the byssai notch, size and shape of short time ranges, the pectens make ideal index species for the auricles, convexity of the valves, shape of the resilial the outcropping strata. The co-existence of planktonic For- insertion, number and shape of the plicae, and in some aminifera with the pectinids in some of the strata allows instances the overall shape of the valves. correlation with European stages. Characters found to be most important for discrimination In most localities the large number of pecten valves at the subspecific and specific levels include the byssai notch, reflects their true abundance in relation to the remainder shape of the resilial insertion, size and shape of the auricles, of the molluscan fauna; but, in some, the relative abundance number and shape of the plicae, and convexity of the valves. of pectens is in part a reflection of diagenetic processes. One new species, Pecten mclellani, is described from the The pectens, along with the oysters and barnacles, have a upper lower Miocene part of the Pungo River Formation exposed at the Lee Creek Mine. It is demonstrated that large amount of calcite in the shell structure and resist Chlamys decemnaria (Conrad) from the Pliocene should in¬ diagenetic processes more strongly than aragonitic-shelled clude C. virginianus (Conrad). A probable intermediate organisms. In many highly permeable coarse-grained sedi¬ form between Placopecten clintonius of early Pliocene age ments, particularly those with large amounts of fragmented and the living P. magellanicus is illustrated and described. shell materials resulting from turbulent conditions during Other rearrangements at the subspecific level are made. deposition, the pectens, oysters, and barnacle plates are the Lectotypes are selected for Pecten yorkensis Conrad ,1867, Pecten eboreus darlingtonensis Dali ,1898 ,Pecten eboreus ur- major recognizable fossil remains. This type of preservation bannaensis Mansfield ,1929 ,Pecten (Chlamys )eboreus bertien- is found in the uppermost bed of the Pungo River Forma¬ sis Mansfield, 1937, and Amusium precursor Dali, 1898. tion in the Lee Creek Mine (unit 7 of Gibson, 1967) where a shell hash is composed almost entirely of barnacle plates and bryozoan tests with lesser numbers of pectens and scattered Ecphora. A similar preservation of calcitic speci¬ Introduction mens is found in the limey indurated layers, units 4-6 of Gibson (1967), in which other molluscan species are repre¬ The Pectinidae (Bivalvia) are one of the most abundant sented by internal molds. In the lower phosphatic sand units and useful groups of mollusks for stratigraphic control of of the Pungo River Formation, however, even the pectens the Cenozoic strata in the Atlantic Coastal Plain. This study have been removed by diagenetic processes, and the only examines the known stratigraphic ranges and paleogeo- specimens recovered are interna lmolds of Pecten humphrey- graphic limits of the species found in the sequence of strata sii, along with internal molds of other mollusks. ranging from lower Miocene to lower Pleistocene at the Many of the pectens have a wide geographic range in Lee Creek Mine, North Carolina, and, also, species from deposits of the Atlantic Coastal Plain. Pecten humphreysii surrounding areas. The ranges are correlated, whenever probably has the widest distribution, from New Jersey Thom a Gs.ibso nU,nite Sdtat eGseologic Saul rve 9y 7,N0ation Galente Rr,eston, southward through Maryland, Virginia, and North Carolina Virg 2in2i0a92. into Florida. Other species range from Maryland or Virginia 31 32 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY southward into Florida, even into south-central Florida. phreysii (Conrad, 1842:194), Argopecten eboreus (Conrad, The pectens must have fairly broad environmental toler¬ 1833:341), and Chlamys decemnaria (Conrad, 1834:151), ances as the same species are found with changing assem¬ three species found in the Lee Creek Mine and treated in blages of other molluscan species. this paper, were named by Conrad. A listing of Conrad’s Another characteristic of pectens in the later Cenozoic of type specimens at the Academy of Natural Sciences of the Atlantic Coastal Plain is their limited stratigraphic Philadelphia and a bibliography are given in Moore (1962), ranges. Most species are restricted to a single formation, with some additional information on type specimens in and some have an even shorter range. The pectens are not Richard s(1968). alone in this rather rapid vertical change, with other mol¬ The molluscan faunas of South Carolina were treated by luscan groups such as Astarte and Crassatella showing Tuomey and Holmes, the initial part of which (1855) in¬ change also; but the pectens are the most conspicuous cluded many of the pectens found in the Yorktown strata group. of the Lee Creek Mine. Emmons (1858) discussed and As a result of their abundance, their widespread geo¬ described many of the vertebrate and invertebrate groups graphic occurrence, and their restricted stratigraphic oc¬ from the Miocene (now recognized as Pliocene) deposits of currence, the pectens are probably the most important eastern North Carolina, including the pectens and named biostratigraphic guide to the later Cenozoic deposits. The one new species. Various groups of mollusks from areas of abundant benthic foraminiferal species tend to have longer the Atlantic Coastal Plain as widely separated as New Jersey ranges than the pectens. This is particularly true in the and Florida were treated by Angelo Heilprin. One of Heil- Pliocene and Pleistocene strata where essentially all the prin’s publications (1881) was concerned solely with the common species range into the Recent. Some of the rarer Tertiary pectens found east of the Mississippi River, and species have more restricted ranges, but are not as desirable this paper touches on most of the pectens found in the Lee for correlation because of their scarcity. The planktonic Cree kMine. foraminiferal species are too rare in almost all of the strata The first comprehensive study of the pectens of the later to be highly useful in correlation within the region. Cenozoic was made by Dali (1898). In addition to describing It is the aim of this paper to give a better understanding species of pectens characteristic of the Florida Tertiary, of the morphologic variation found within the various spe¬ Dali treated many species from North Carolina, Virginia, cies of pectens that occur in the Pungo River and Yorktown an dMaryland. formations in the Lee Greek Mine and their closely related The Maryland Geological Survey’s volume on the Mio¬ species, both by quantitative methods and illustration of the cene deposits of that state (Clark, 1904, with parts prepared variations. by various authors) is an amazingly complete study of the fauna of the Chesapeake group. The pectens are included Previous Work in the section on the Pelecypoda by Glenn (1904) for that volume. Later, a study of the Coastal Plain of Virginia was The fossiliferous bluffs along Chesapeake Bay and its published (Clark and Miller, 1912) and also one of the tributaries long have been famous collecting sites for Ter¬ Coastal Plain of North Carolina (Clark et al., 1912). These tiary fossils. The first illustrated fossil invertebrate from latter two volumes deal with the stratigraphy of the Miocene North America was probably from the Atlantic Coastal and Pliocene deposits, but the invertebrate faunas are pre¬ Plain deposits of the Chesapeake group. A pecten, later to sented only in the form of lists and charts. be named Pecten jeffersonius, was illustrated by Lister in Several publications by Axel Olsson, particularly those 1687 (see Ward and Blackwelder, 1975:3, 15, pi. 1; Wilson, dealing with the molluscan species from the Yorktown p. 21 herein). The pectens were among the earliest species Formation in Virginia (Olsson, 1914, 1917), added new described because of their large size and great abundance information on the pectens and knowledge of the general in the strata of Maryland, Virginia, and North Carolina. age and faunal relationships of the strata. Helen Tucker- Say (1824) described three of the most common and impor¬ Rowland (1934, 1936a, 1936b, 1938) covered most of the tant species o fpectens ,Pecten jeffersonius ,P .madisonius ,and species of pectens from the Cenozoic deposits of Eastern P. clintonius, naming them after famous Americans of that North America, both reviewing older species and describing time. The type suites of these species were deposited in the new taxa. During the same period, W.C. Mansfield worked British Museum, and type specimens were recently selected on the Miocene and Pliocene deposits in North Carolina and illustrated by Ward and Blackwelder (1975). and Virginia and described several new species and subspe¬ Most of the early descriptions of the marine mollusks cies of pectens (Mansfield, 1929b, 1936, 1937). The infor¬ from the Atlantic Coastal Plain Cenozoic deposits were mation obtained from the biostratigraphic distribution of made by Timothy Abbott Conrad. Conrad made far-rang¬ the pectens was of great importance in his development of ing collecting trips and published numerous papers from a zonal concept for the Miocene and Pliocene strata of the 1830s to the 1870s describing the faunas. Pecten hum- Virginia and North Carolina (cf. Mansfield, 1929a, 1944). NUMB E6R1 33 Pectens from the older Miocene strata in Maryland, par¬ ticularly the Calvert and Choptank formations, were rede¬ scribed by Lois Schoonover (1941). Julia Gardner’s (1944, 1948) descriptions of the molluscan fauna from the Miocene and Pliocene strata of North Carolina and Virginia illustrate many of the molluscan species, including many of the im¬ portant species of pectens. Although this work does not include all the molluscan species found in the Yorktown strata in Virginia and North Carolina, it is by far the most extensive study to date. Richards (1950) presented collecting localities, a partial faunal list, and illustrations of some of the more common species of mollusks, including pectens, from the coastal plain of North Carolina. Mongin (1959), in her comparison of molluscan species from the Miocene and Pliocene of North America with those of Europe, discussed various species of pectens that are found in the Lee Creek Mine. A comprehensive study of the evolution of the Argopecten gibbus group from Cenozoic strata of eastern North Amer¬ ica, based upon the multivariate study of population mor¬ phology through time, was made by Waller (1969). Recently Ward and Blackwelder (1975) separated Atlan¬ tic Coastal Plain species formerly assigned to Lyropecten, an endemic Pacific Coast genus, into their new genus Chesa- pecten. Several of the species found in the Lee Creek Mine belong in Chesapecten :C .coccymelus ,C .nefrens ,C .jefferson- ius, and C. madisonius. They also refigured some of the Say (1824) types from the British Museum and renamed some of the species of pectens because of nomenclatorial prob¬ lems. Collecting Techniques In the early stages of mining operations by Texasgulf Inc. at Lee Creek (Figure 1), a small test pit several hundred yards in length and width was opened in an area subse¬ quently mined out and now reclaimed. The pit was dug by Figur e1.—Locatio no mf ajo lrocalitie asn dformationa ulnit dsiscusse din a floating dredge that, with the help of other pumps, low¬ text 1: =Kirkwood Formation in vicinit yo Sf alem and Jericho N, ew Jersey; ered the water level in the pit as it dug. The dredge 2 =Calvert C, hoptank a, nd St M. ary sformation sa tCalver tCliffs M, ary¬ frequently needed maintenance or underwent repairs and land ;3 = Yorktown Formation along Chowan River N, orth Carolina 4 ,= thus ceased pumping water out of the test pit. Even though Le eCree kMine N, ort hCarolina 5; =Waccamaw Formatio ni nsouthernNorth Carolin aan dnorthern South Carolina 6; =Torreya C, hipola O, ak other pumps continued working, with the dredge not work¬ Grove a,n dJackso nBlu fformation si n orthwester nFlorida 7=;Caloos- ing, water level rose in the pit by as much as 30 feet (9 m). ahatch eFeormatio sinouthe rFnlorida. The rising water level cleaned the near-vertical sides of the pit, and resumption of pumping by the dredge permitted detailed inspection of the stratigraphic units in the walls. The newly cleaned and emerged walls were examined for fossils, and careful stratigraphic collections were made. The author spent numerous days collecting during the winter of 1963-1964, and the stratigraphic information gained forms the basis of the placement of lithologies into the sequence presented in Figure 2. The lithologies vary among the different parts of both the Pungo River and Yorktown formations. The Pungo 34 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY m 3.35 Buff to yellow cross-bedded medium sand 1.64 Blue silty and clayey sand, abundant shells (Unit 9) 3.65 Blue to greenish blue slightly silty medium to coarse sand, abundant shells and corals (Unit 3) mm 1.22 Blue sand with 0.5m boulders of well-indurated 0.91 quartz sandstone, abundant shells (Unit 7)Blue silty sand, abundant shells (Unit 6) 7.01 Blue silty and clayey fine sand, scattered calcitic shells and barnacles, lenses of rotten Turritella (Unit 5) PLEI SF TOY FROF OMCR REK.ANIMOVTEOEPAIORUTWAINONGNO 1.63 Blue silty and clayey fine sand, abundant rottenTurritella . common pectens (Unit 4) 0.61 Blue silty fine sand, common pectens (Unit 3) q3ioV°ioro % GoV% oO S° Boq30 Blue silty and clayey fine sand, abundant echinoid spines, rO QOi G OQe B OQ. lO O OQO O oOQ < 3.05 scattered shells and barnacles, phosphate and quartz O O 0 cQQa^.o.* pebbles in lower 1 m (Unit 2)0.30 Blue silty sand, large phosphate pebbles ar d bone, shells (Unit 1) 1.07 Yellow-green silty and clayey sand, abundant bryozoan fragments (Unit 7) r wo 0.76 Yellow-green sand, hydrozoan fragments interbedded with dark phosphatic lenses 0.91 Gray phosphatic sandy limestone, molluscan molds and casts (Unit 5) (Unit 6) 0.91 Interbedded gray phosphatic limestone and dark brown phosphatic sands (Unit 4) B 6 o ooo od f OrfV -0V 1.52 Dark greenish brown silty medium grained phosphatic sands (Unit 3) 0.91 Greenish gray indurated diatomaceous clay (Unit 2) 0A,iA , Wo Q W Ay a Vo ^ AV aoP' < o°c| ( rp-O > Vo Wcnoo o' W0 o o’ .o0OO OoG 0 OG O 7.14 O O 0 &0 t Dark greenish brown medium to fine phosphatic sand (Unit 1)WWo°flWW3 ̂O oO BQ CW OJ O P S3 O Q GG G © O0 G Q O_ O < OQ O ©_ 5' O GOOO (‘©WJ h 0o ®O0 GQ Q0 O7©O Q O 0 OoOG 0” OO O o P Q€Oo o j>d o o e op sVi ' Figur e2.— Section o fMiocen eand younge rstrat aexposed in th enorthwes twa lol fth etes tpit L, e eCree kMine. I he lower units of the Yorktown Formation are bluish diagenetically altered to a chalky and partially dissolved clays and sands containing large amounts of secondary appearance, and near the lop the beds are partially indu¬ phosphatic material (irregularly shaped, black in color), rated because of the local redeposition of the carbonate which rapidly decreases in size above the base; overlying from the shells. this is a sequence with abundant echinoid spines in a fine With the beginning of mining operations several years quartz sandy matrix, the abundance of spines sometimes later, vast amounts of the Pungo River and Yorktown giving a fibrous appearance; tbe next sequence upward has formations were exposed in the spoil piles derived from the large numbers of Turritella, which generally have been dry stripping operations. Because of the large size of the NUMB K6R1 35 drag-line bucket (72 cubic yards; 55 cubic meters) and the Maryland. The types of lithologies are different, phosphatic careful stripping of the layers, material from the same sands in the Pungo River Formation and clayey sands and stratigraphic intervals tends to be localized on the spoil diatomaceous clays in the Calvert Formation, but a similar piles. The localized material can be placed within the strat¬ time span for the two formations rather than just a slight igraphic sequence by comparison of the lithologies and overlap of part of one formation with a part of the other is faunas with the known distribution in the outcrop sequence indicated. Gibson (1983a:38, 63; 1983b:359) has found in the walls of the test pit, and thus into the distinctive unit younger parts of the Pungo River Formation to the north sequence of Gibson (1967). Although some of the measured and east of the section in the mine, and these strata appear and illustrated specimens were collected in place from the to be younger in age than any part of the Calvert Formation w'alls of the test pit or large mining pit, most specimens are so far dated. from the spoil piles; the great amount of areal exposure of The age significance of the planktonic Foraminifera of the units uncovered many well-preserved specimens from a the Pungo River Formation was discussed by Gibson (1967; relatively narrow and known stratigraphic interval. 1983b). The assemblages from the Pungo River Formation on which ages were obtained occur in the upper part of the Correlation formation. These assemblages are referable to zones N8 or possibly early N9 in the Neogene planktonic scale (Blow, Most of the species identified to date from exposures of 1969:229, 230), which is presently accepted as approximat¬ the Pungo River Formation in the Lee Creek Mine also are ing the early to middle Miocene transition (Blow, 1969:203, found in the Calvert Formation of Maryland and Virginia. 265ff; Berggren and Van Couvering, 1974:202, 271ff). Three species ,Chesapecten coccymelus ,Ostrea percrassa ,and The foraminiferal assemblages in the lower and middle Ecphora tricostata are restricted elsewhere to the Calvert parts of the formation are too poorly preserved to be Formation in Maryland and Virginia and the coeval Kirk¬ identifiable. A similar assemblage referable to zone N8 or wood Formation in New Jersey. Chesapecten nefrens from N9 also is found in bed 10 of the Calvert Formation in the uppermost part of the Pungo River Formation in the Maryland (see Gibson 1 983b:360), and thus these two parts mine is restricted to the upper part of the Calvert Formation of the two formations have a similar age, approximating the and the Choptaj^ Formation in Maryland and northern early to middle Miocene boundary. Virginia. The other species of mollusks reported to date The time ranges of Chesapecten coccymelus and C .nefrens from the Pungo River Formation include Pecten mclellani, thus seem to be similar in the different geographic areas. new' species, and tw'o new species of Ecphora: E. pamlico (p. Pecten humphreysii also appears to have a similar range in 24) and E. aurora (p. 24), which in North America are North Carolina, Virginia, Maryland, and New Jersey, oc¬ restricted to the Lee Creek exposure of the Pungo River curring in what are considered to be generally time-equiv¬ Formation. alent strata (Gibson, 1967:636; 1983a:38). Banks and The three species restricted to the Calvert Formation Hunter (1973) reported this species from the Torreya For¬ and the one species that ranges from the Calvert into the mation in Florida, and some of their specimens are illus¬ Choptank Formation permit correlation of the Pungo River trated in the present paper (Plate 4: figures 4-6). (The Formation in North Carolina with the Calvert Formation Torreya Formation of Banks and Hunter (1973) is herein in Maryland. The similarity of the span of time represented adopted for U.S. Geological Survey usage.) The strata in in the two formations is unknown at present, but evidence w'hich they occur, however, are tentatively assigned by them to date from the pectens suggests that they have a similar to the planktonic foraminiferal zones N5 and N6, consid¬ time span. The Calvert Formation in Maryland consists of erably older than the present ages known for the strata 16 beds (zones 1-16 of Shattuck, 1904). Pecten humphreysii bearing P. humphreysii in the Lee Creek Mine and north¬ is known from beds 1-10, the lower and middle part of the ward (N8 and N9). The age of the Torreya Formation may Calvert. Chesapecten nefrens occurs in bed 14 and ranges be refined upward, but if not, it will mark a significantly upward into the Choptank Formation. The specimens from older occurrence of P. humphreysii in Florida than presently the Lee Creek Mine are from the uppermost beds of the known in the North Carolina-Maryland area. Another pos¬ Pungo River Formation. Thus the superposition of the two sibility is that the low er part of the Calvert and Pungo River species in the Pungo River Formation at the Lee Creek formations, which are not dated by planktonic Foraminifera Mine is the same as in the Calvert, with an indicator of bed because of lack of specimens and/or poor preservation, 10 or older strata ( Pecten hymphreysii ) being overlain by an could be of an age older than N8, thus similar to the indicator of bed 14 or younger ( Chesapecten nefrens). The Torreya. considerable thickness of strata below r the occurrences of The upper part of the Yorktown Formation in Virginia Pecten humphreysii in the upper middle part of the Pungo and North Carolina has been correlated with the Duplin River Formation may correspond to the time represented Formation of the southern part of North Carolina and by the strata below bed 10 of the Calvert Formation in adjacent Georgia (Mansfield, 1944, table 1). The Ecphora 36 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY and Cancellaria zones of the Choctawhatchee Formation in with the Croatan Formation (Hazel, 1983:84-85). Florida were correlated with the Yorktown Formation by The upper part of the Croatan Formation is correlated Mansfield (1944, table 1). The Choctawhatchee Formation with the Waccamaw Formation, and both formations are has been reinstated, redefined, and stratigraphically re¬ considered time-equivalents of the Caloosahatchee Forma¬ stricted to include only the lower part of former usage by tion in Florida. There are seven species of pectens in com¬ tbe U.S. Geological Survey; its upper part, the Ecphora and mon between the Waccamaw and Caloosahatchee forma¬ Cancellaria zones, is now placed in the Jackson Bluff For¬ tions: Pecten brouweri, P. raveneli, Argopecten eboreus, A. mation of Puri and Vernon (1964). A number of pectens vicenariu sS,tralopecte nernestsmith Li,eptopecte nleonensi sa,nd restricted to the Yorktown Formation in Virginia and North Amusium mortoni. Two of these species are restricted to the Carolina are also found in the Jackson Bluff Formation. Waccamaw and Caloosahatchee formations ,Stralopecten er¬ The yinclud eChesapecten jeffersonius A, rgopecten eboreu swat- nestsmithi and Pecten brouweri, and support the correlation sonensis, and A. comparilis. These species support the cor¬ of the two units. The planktonic Foraminifera support a relation of these formations. correlation with the early Pleistocene zone N22 for part, at Mansfield (1936, 1944) divided the Yorktown Formation least, of the Waccamaw and Croatan formations, with a in Virginia and North Carolina into two zones. Zone 1 or probable late Pliocene age or zone N21 for the remainder the Pecten clintonius zone is overlain by zone 2 or the (see Gibson ,1983b:364). Turritella alticostata zone, which is composed of three sets of beds. Units 1 and probably all of 2 of the Yorktown Biostratigraphy of the Pectinidae Formation in the Lee Creek Mine of Gibson (1967; see also Figure 2) belong to Mansfield’s zone 1, and the overlying The pectens, as already noted, are ideal guide fossils to units 3 to 5 belong to zone 2. the upper Cenozoic deposits of the Atlantic Coastal Plain. Planktonic Foraminifera from zone 1 of the Yorktown in Species range zones often coincide with formational bound¬ the northern part of North Carolina and in the Lee Creek aries, which is not surprising as the formations characteris¬ Mine are of an early Pliocene age, planktonic zone N19/ tically used in the Atlantic Coastal Plain are in most in¬ N20 (Gibson, 1983b:363). Mansfield's zone 2 belongs to stances biostratigraphic rather than lithostratigraphic units. younger parts of zone N19/N20 and probably extends into Thus, the pectens are one of the most prominent markers zone N21 (late Pliocene). of the biostratigraphic “formations.’ In addition, changes The upper part of the fossiliferous strata in the Lee Creek in the assemblage, either at the specific or subspecific level, Mine, termed the upper shell bed (units 8 and 9 of Gibson, sometimes allow further biostratigraphic subdivision within 1967) was included in the Yorktown Formation by Gibson aformation. (1967) because it appeared to be the youngest part of the The following sequence of pectens may be used to sub¬ depositional cycle of later Cenozoic strata in eastern North divide the strata of the Chesapeake group, starting from Carolina. Other strata of a similar age are found at Mt. the basal unit, the Calvert Formation (Figure 3). Gould Landing along the Chowan River in northeastern Pecten humphreysii and Chesapecten coccymelus are re¬ North Carolina (Figure 1), and these were also placed in stricted to the lower and middle part of the Calvert For¬ the upper part of the Yorktown Formation by Mansfield mation in Maryland, occurring from bed 1 to bed 10, and (1944) (although given a younger age than the classic York¬ to the Pungo River Formation in North Carolina. The town by Hazel, 1971). The upper shell bed (units 8 and 9) upper part of the Calvert Formation and the overlying and the underlying boulder bed and fossiliferous bed (units Choptank Formation are characterized by the occurrence 6 and 7 of Gibson, see Figure 2) appear to be part of a of Chesapecten nefrens, which also occurs in the uppermost sequence that is separated from the rest of the Yorktown part of the Pungo River Formation in North Carolina. The by an unconformity. The age of these strata is younger than St. Marys Formation in Maryland is characterized by Ches¬ that of the typical Yorktown beds in most of North Carolina. apecten santamaria ,with a change in the species morphology These units are probably time-equivalents of the Croatan upward through the beds. Strata of the Maryland St. Marys Formation, the type area of which is slightly south of the and Choptank formations are not known south of northern Lee Creek Mine, and the Waccamaw Formation, which is Virginia (Gibson, 1970). The St. Marys Formation in Vir¬ exposed in southern North Carolina and northern South ginia (considered the basal part of the Yorktown Formation, Carolina (Figure 1). As the lithology is similar to that of the Gibson, 1971) is marked by the occurrence of Chesapecten Croatan Formation, which is probably in the same deposi¬ middlesexensis throughout the formation, although with a tional basin (Gibson, 1983a:74; 1983b:364), the upper part series of morphologic variations, and in its upper part by of the fossiliferous strata in the mine, units 6-9, is assigned Argopecten eboreus urbannaensis and Placopecten clintonius to the Croatan Formation. The James City Formation of rappahannockensis .Both Chesapecten santamaria and C .mid¬ Du Bar and Solliday (1963) is considered to be synonymous dlesexensis show considerable variation throughout their NUMB E6R1 37 N S Figur e3 —. Rang echar to tfh ecommon lat eCenozoi cpecten specie soccurring in th eformation so tfhe centr Aaltlan tCicoast Palain. chronologic range, and further subdivision of the strata also an important index to this part of the section. ma ybe possible. The upper part of the Yorktown Formation is character¬ The lower beds of the Yorktown belonging to zone 1 of ized by some of the more advanced forms of Argopecten Mansfield, are characterized by the occurrence of Placopec- eboreus eboreus ,A .eboreus bertiensis in a few localities along ten clintonius clintonius along with the first appearance of with A. eboreus aff. A. eboreus solarioides, advanced forms of Chesapect ejenffersoni ujesffersonius. Chesapecten madisonius, along with a very few advanced In the middle part of the Yorktown Formation, the lower specimen so fC .jeffersoniu sseptenarius. part of Mansfield’s zone 2, the Chesapecten stock changes to The younger Croatan and Waccamaw formations contain C .jeffersonius septenarius and C .madisonius .Other subspe¬ new group ssuch a sPecten brouweri ,Stralopecten ernestsmithi, cies of Argopecten eboreus become diagnostic, such as A. Argopecten vicenarius ,along with the abundant specimens of eboreus watsonensis in the lower middle part, giving rise to the various subdivisions of A .eboreus solarioides. A. eboreus eboreus in the middle part. Chlamys decemnaria is Other species of pectens are found in the strata of the 38 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY mys decemnaria and Amusium, the other two groups found in the Lee Creek Mine. Although phylogenies have been developed for late Ter¬ tiary pectens, little has been determined concerning the origin of the groups. The absence of information is due both to the lack of strata of immediately preceding age (upper Eocene, Oligocene, and lower Miocene strata are poorly represented in the central and northern Atlantic Coastal Plain) and also to the lack of knowledge of the faunas existing in older strata. The pectens found in strata of late Eocene and Oligocene age are quite different from those found in the lowermost Miocene deposits of the Calvert and Pungo River formations. The earlies trecognized representatives o fthe Chesapecten stock appear in the Calvert Formation in Maryland and Virginia. If the ancestral forms were confined to the central and northern parts of the Atlantic Coastal Plain because of environmental restrictions, determining them will be diffi¬ cult because strata of Oligocene and early Miocene age crop out in only one place in this area. In North Carolina, Oligocene and possibly lower Miocene strata are present, but forms ancestral to the Miocene pectens have not been reported. It may be necessary to look to other areas, possibly Florida, to find the ancestral forms that later moved north¬ ward into this area. Therefore, at the present time, while phylogenies have been proposed for most groups, early Tertiary ancestral group sremain unrecognized. Figur e4.— Distribution o fspecie so fpecten sin th etes tpi tstrat ao fthe Le Ceree Mk ine. Biogeography and Paleoclimate For many years, probably since Dali (1904), the environ¬ Chesapeake group; however, they are either rare or their ment during deposition of the lower Miocene deposits of range is uncertain at the present time. Distribution of Florida (of Dali, now in part Pliocene) was considered to be species in the Lee Creek Mine is given in Figure 4. very warm, followed by progressive cooling. After the early Miocene, cooling presumably would lead to the southward Phylogeny of the Pectens migration of the faunas found in the Chesapeake area, possibly resulting in a mixing of the more northern species Although Dali (1898) and subsequent workers mentioned with the indigenous Florida assemblages. A result of this relationships among the various groups of pectens, Mans¬ faunal migration would be strong provincialism in the field (1936) developed the first extensive phylogenies of the northern earlier Miocene faunas, such as those of the Cal¬ late Tertiary pectens of the Atlantic and Gulf Coastal plains. vert compared to those of the Chipola or Oak Grove for¬ Modifications have been made in some of the lineages, but mations of Florida in contrast to the more widespread in large part Mansfield’s phylogenies still are generally distribution of the faunas in the later deposits considered accepted. Waller s (1969) detailed phylogeny of the Argo- Pliocene in this volume. pecten gibbus stock, however, involved changes from that of The faunal provincialism between the Chipola (lower Mansfield. Miocene) and/or Oak Grove (middle Miocene) formations In the present paper, the species stocks and their inferred of Florida and the more northern Calvert Formation is well phylogenies are given, when possible, in the discussion of marked by the distribution of the mollusks in the two areas. the individual species and also summarized in Figure 5. The exact correlation of these units is uncertain at this time, Phylogenies have been proposed, either in Mansfield (1936) because some authors regard the Chipola as being slightly or herein ,for the Chesapecten group ,the Argopecten eboreus older than the Calvert, and the Oak Grove Formation as stock, the Placopecten group, and the probable Pecten mclel- feeing more or less equivalent to the Calvert (Mansfield, lani lineage. Phylogenies have not been developed for Chla- 1944). Correlations place the Hawthorn Formation in Flor- NUMB E6R1 39 Figur e5 —. Phylogen yo sfom epecte nspecie soccurrin gi nMiocen ethroug hlowe Pr leistocen estrat ain the Atlanti cCoasta Pl lain T. he placemen to fthe boundar ybetween zone 1 and zone 2 o fthe Yorktown Formatio inusncertai na ,itsh reelationsh ibpetwee Pnecte hnumphreys aiin Pdm. clellani. ida and southern Georgia as at least in part equivalent in Formation, including one species that also occurs in the age to the Calvert (Gibson, 1967), a correlation given some Chipola Formation (Dali, 1898:775, 729; Gardner, additional support by the newly noted occurrence in both 1926:45, 46, 49, 50; Tucker-Rowland, 1938:12, 13, 70): formations of Chlamys nematopleura Gardner (Druid Wilson, Chesapecten sayanus (Dali ,1898) ,Nodipecten condylomatus pers. comm., 1976). The Hawthorn appears to be at least (Dali, 1898), Pseudamusium diktuotum Gardner, 1926, and in part of the same age as the Chipola (Gibson, 1967). Pseudamusium sp .of Gardner ,1926. A search of the literature and the USNM collections was Five species of pectens are found in the Calvert Formation made to determine correlation of the pecten assemblages (Dali, 1898:720, 741, 753; Glenn, 1904:372, 373, 374; between the various Neogene formations in Florida, North Schoonover, 1941:188, 201; Tucker-Rowland, 1936a:478, Carolina ,and Maryland. 1936b:1007, 1938:68; Ward and Blackwelder, 1975:8, 9): The following six species of pectens have been reported Pecten humphreysii Conrad, 1842, Chlamys nematopleura from the Chipola Formation (Dali, 1898:720, 729, 733, Gardner, 1936, Chesapecten coccymelus (Dali, 1898), C. nef- 740, 755; Gardner, 1926:44, 46, 47, 50; Tucker-Rowland, rens Ward and Blackwelder, 1975, and Pseudamusium ceri- 1936a:478, 1936b: 1007, 1938:11, 58): Pecten burnsn Dali, nus (Conrad ,1869). 1898, Chlamys acanikos Gardner, 1926, C. alumensis (Dali, The Pungo River Formation, from the only known out¬ 1898), “ Chlamys ” chipolana (Dali, 1898), Nodipecten condy- crop in the Lee Creek Mine, also contains five species of lomatus (Dali, 1898), and Amusium precursor Dali, 1898. pectens (Gibson, 1967:636, and this paper): Pecten mclellani, Four species of pectens are reported from the Oak Grove new species, P. humphreysii Conrad, 1842, Chesapecten coc- 40 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY cymelus (Dali, 1898), C. nefrens Ward and Blackwelder, The following seven species of pectens have been re¬ 1975 ,and Amusium sp. ported in the Ecphora and Cancellaria facies of the Jackson There are no species in common between the Chipola or Bluff Formation of Florida; only these two facies are consid¬ Oak Grove formations in Florida and the Pungo River ered coeval with the Yorktown formation (Gardner, Formation in North Carolina or the Calvert Formation in 1944:34, 36, 37, 39; Mansfield, 1932:56-65; Tucker-Row¬ Virginia and Maryland. The complete difference in assem¬ land, 1936a:480, 481, 482, 1938:33, 40, 59; Waller, blages supports the inference of a high degree of provin¬ 1969:52, 59): Pecten ochlockoneensis Mansfield, 1932, Fla- cialism in Calvert-Chipola-Oak Grove time. The Chipola bellipecten macdonaldi (Olsson, 1922), Argopecten eboreus Formation is considered to be of very warm water origin (Conrad, 1833),/!. comparilis (Tuomey and Holmes, 1857), with a number of tropical elements in the molluscan fauna. Chesapecten jeffersonius (Say ,1824) ,Leptopecten leonensis The Calvert Formation is of a cooler environment; just how (Mansfield, 1932), and Amusium mortoni { Ravenel, 1844). much cooler is a matter of some controversy. Gibson (1962) Four of these species are found in both the Yorktown considered the foraminiferal fauna of the Calvert Forma¬ and Jackson Bluff formations. They are Argopecten eboreus, tion to be of a temperate nature, probably similar to the A .comparilis C, hesapecten jeffersonius a, nd Amusium mortoni. conditions presently existing off the Maryland coast today. This is in marked contrast to the Calvert and Chipola The basis for this conclusion was that, of the 41 species of formations of early and middle Miocene ages, during w'hich Foraminifera found in the formation, 7 are living species time there were no species in common betw'een the tw'o characteristic of temperate waters, while none of the living areas. species are of exclusively warm water distribution (restricted It is important to determine whether this overlap is the to areas south of Cape Hatteras). However, F.C. Whitmore result of a southward migration of the Chesapeake area (pers. com., 1974) considers the Calvert Formation to rep¬ pectens into Florida, as postulated by Dali (1904), and thus resent a warm to possibly subtropical environment based a cooling trend, or a northward migration of species from upon the vertebrates, including crocodiles and otoliths. Florida, indicating a warming trend through the Coastal Whatever the climatic conditions may have been, there Plain as postulated by Gibson (1967) and Hazel (1971). The were considerable differences between Florida and the geologic record is reasonably good between the Calvert to Chesapeake Bay area, which resulted in the provincialism Yorktown ages in the Chesapeake area and the Chipola to of the pectens and other molluscan and foraminiferal Jackson Bluff ages in Florida. An examination of the origins groups. The difference between the pectens of the Calvert of the four common species suggests that there was move¬ and Pungo River formations and those of the Chipola and men tboth ways. Oak Grove formations in Florida indicates that the main The earliest recognized members of the Chesapecten stock provincial barrier was south of central North Carolina. This are C. coccymelus in the Calvert and Pungo River formations supports the similar conclusion of Gibson (1967), based of late early to early middle Miocene age and C. sayanus in upon the benthic and planktonic Foraminifera, that the the Oak Grove Formation of early middle Miocene age main provincial boundary was to the south of the Lee Creek (Huddlestun, 1976). Correlations would suggest that the Mine. northern occurrences are slightly older. Although C. jeffer¬ Later, in the Miocene and Pliocene (i.e., Yorktown), sonius is found both in the Chesapeake area and Florida, according to Dali (1904), a southward migration of the the development of C. middlesexensis from w'hich it came is species from the Chesapeake area took place, leading to the mainly or solely in the Chesapeake area and would seem to presence of cooler water species in the Florida area. This indicate a southward migration of this species group into hydroclimatic change would lead to a lesser amount of Florida. provincialism, and this change is reflected in the pecten Although the early members of the Argopecten gibbus assemblages. stock are characteristic of the Florida area, it appears that Nine species of pectens from the Yorktown Formation the earliest recognized member of the A. eboreus lineage have been reported in the literature or are in the USNM within that stock, A. eboreus urbannaensis, is found in the collections of the National Museum of Natural History Chesapeake area (Waller, 1969). The later development of (Dali, 1898:722, 725, 730, 741, 749, 750, 757; Gardner, A. eboreus would indicate a southward movement of the 1944:30, 31,32, 34, 36, 37, 39; Mansfield, 1936:178-180; stock and diversification into a number of forms. If A. Tucker-Rowland, 1936a:480, 1936b: 1008, 1009; 1938:15, eboreus urbannaensis belongs to a separate lineage from the 19, 33, 38, 40, 52, 59; Waller, 1969:52, 59; Ward and other forms placed in A. eboreus, then the earliest member Blackwelder, 1975:13): Pecten smithi Olsson, 1914, Chlamys o fthe A .eboreus stock would be A .eboreus watsonensis ,w'hich decemnaria (Conrad, 1834), C. rogersii (Conrad, 1834, Ar¬ appeared at approximately the same time both in Virginia gopecten eboreus (Conrad ,1833) ,A. comparilis (Tuomey and and Florida from southern ancestry. Holmes ,1857) ,Placopecten clintonius (Say ,1824) ,Chesapec- Argopecten comparilis is a phyletic descendant of A. choc- ten jeffersonius (Say, 1824), Leptopecten sp., and Amusium tawhatcheensis (Mansfield) according to Waller (1969:27). morton i(Ravenel ,1844). The latter species is found only in Florida, and thus the NUMB E6R1 41 immediately following A. comparilis, which is found at ap¬ 1936:181-183; Olsson and Harbison, 1953:53-56; Tucker- proximately the same time in both Florida and Virginia- Rowland, 1936a:483, 1936b: 1010, 1938:25, 27, 28, 34, North Carolina, would have southern ancestry. 39, 59; Waller, 1969:50, 51, 59): Pecten brouweri Tucker, Amusium mortoni presents a complex problem in terms of 1934, P. exasperatus (Sowerby, 1843), Euvola raveneli (Dali, occurrences. Although specimens of A. mortoni have been 1898), Argopecten anteamplicostatus (Mansfield, 1936), A. reported from pre-Yorktown beds in tbe Chesapeake area eboreus (Conrad, 1833), A. vicenarius (Conrad, 1843), Chla- (Dali, 1898:757; Gardner, 1944:39), Mansfield (1932:65) mys harrisii (Dali, 1898), Stralopecten ernestsmithi (Tucker, restricts the species to Yorktown-Jackson Bluff and younger 1931), S. caloosaensis (Dali, 1898), Leptopecten leonensis strata, correctly crediting the older reported occurrences (Mansfield, 1932), L. wendelli (Tucker, 1934), Nodipecten of misreading of localities (see discussion under Amusium nodosus (Linnaeus, 1758), and Amusium mortoni (Ravenel, sp.). Mansfield (1936:180) lists A. mortoni as occurring only 1844). in the younger part of the Yorktown, while occurring in Of the 11 species of pectens reported from the Wacca¬ the slightly older Ecphora zone of the Jackson Bluff For¬ maw Formation and its equivalent in North Carolina, the mation. If this correlation is valid, A. mortoni first appeared Croatan Formation, three species are restricted in their in Florida and moved into the Chesapeake area later in known distribution to the Waccamaw. They are Pecten Yorktown time. Huddlestun (1976), however, reported the hemicyclicus “, Pecten ”holmesi ia, nd Leptopecten auroraensis. Jackson Bluff to be of late Zanclian age; if so, this age would All of the remaining eight species are found also in the place it very close to the age of the Yorktown strata in Caloosahatchee Formation, making a remarkable similarity which it occurs, indicating a similar time of origin in the between the two areas, and indicating very little provin¬ tw aoreas. cialism in the pectinids at this time along the Atlantic Coast Therefore, of the four groups, one, Chesapecten jefferson- between Florida and North Carolina. ius ,is a southward migrant; one ,Argopecten eboreus ,a prob¬ Thus from the middle Miocene to the early Pleistocene able southward migrant; one, A. comparilis, a probable there is an increasing number of species in common between northward migrant; and one, Amusium mortoni, a possible the North Carolina-Maryland and Florida areas. What this northward migrant. Thus, in the pectens, the similarity in means with regard to temperature relationships is somewhat the fauna is due to a two way movement between Florida conjectural, but it would appear that the strong provincial¬ and the Chesapeake area. The movement may have been ism between the Chipola and Oak Grove formations with a facilitated by the change in the paleoclimate during York¬ generally subtropical nature and the Calvert would mark town time. The Chesapeake area during early Yorktown the Calvert as cooler; whether this would be warm temper¬ time is postulated as being cool with a warming trend ate or cool temperate for the Calvert is unsettled at present. upward through Yorktown time (Gibson, 1967; Hazel, The decreasing provincialism higher in the column, with 1971), which could have been a cause of decrease in provin¬ the Waccamaw fauna having most of its pecten species in cialism during this time interval. common with the Caloosahatchee while the latter still re¬ The Waccamaw Formation in North and South Carolina tains a subtropica lcharacter ,suggests a considerable warm¬ and the Caloosahatchee Formation in Florida are here ing of the North Carolina area. considered coeval units. All reports of occurrences of pec¬ tens from the literature and from the USNM collections Diversification of the Pectinids were noted in order to compare the degree of similarity between the two areas. The faunal list of pectens from each of the formations The Waccamaw Formation, including Croatan Forma¬ gives information on the diversity of one group of mollusks tion at the Lee Creek Mine, contains 11 species of pectens between the more southerly and more northerly parts of (Ward and Blackwelder, this volume; Dali, 1898:721, 751; the Coasta lPlain strata. Gardner, 1944:31, 34, 36, 39; Mansfield, 1936:181-183; The surprising observation is that although the Chipola Tucker-Rowland, 1936a:484, 1938:24, 27, 50, 59; Waller, Formation is considered to have been deposited in consid¬ 1969:49, 51, 59): Pecten brouweri Tucker, 1934, P. hemicy- erably warmer environmental conditions, the number of clicus Ravenel, 1834, “ Pecten ” holmesii Dali, 1898, Euvola species of pectens is just one greater than is found in the raveneli (Dali, 1898). Argopecten anteamplicostatus (Mans¬ Pungo River or Calvert formations 500 miles (805 km) to field, 1936), A. eboreus (Conrad, 1833), A. vicenarius (Con¬ the north. The Oak Grove Formation, which is also consid¬ rad, 1843), Stralopecten ernestsmithi (Tucker, 1931), Lepto- ered coeval with the Pungo River-Calvert strata, has one pecten leonensis (Mansfield ,1932) ,Leptopecten auroraensis less species than the formations found farther north. Many Ward and Blackwelder, this volume, and Amusium mortoni complex factors are involved in a list of species from a (Ravenel ,1844). formation, such as the geographic area covered, the availa¬ The Caloosahatchee Formation contains 13 reported spe¬ bility of outcrops, the variety of facies, and the amount of cies of pectens (Dali, 1898:721,728, 731,742, 757; DuBar, collecting, study, and publication. With the present infor¬ 1958:158-161; Gardner, 1944:30, 31, 36, 39; Mansfield, mation, however, the common biological phenomenon of 42 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY increasing numbers of species with decreasing latitude is not observed in the pectens of the Chipola-Oak Grove, Calvert-Pungo River interval. A similar paradoxical situation exists in the Yorktown- Jackson Bluff time interval. The Yorktown Formation in the more northerly area contains nine species of pectens, whereas the equivalent Ecphora and Cancellaria facies of the Jackson Bluff Formation in Florida contain only seven spe¬ cies. However, during deposition of the uppermost Pliocene and lower Pleistocene strata the general biologic pattern of more species in the more southerly areas is marginally present, as 13 species of pectens are found in the Caloosa- hatchee Formation in Florida, whereas only 1 1 species are found in the Waccamaw-Croatan formations in North and South Carolina. An interesting point is the increasing diversity of the species of pectens with time. Considering the known out¬ crops of the formations, it is probable that similar numbers of facies are represented at the different time intervals and have been more or less equally studied. Yet, the oldest Miocene assemblages consist of four to six species, increas¬ ing from seven to nine during Yorktown-Jackson Bluff Figur e6.— Diagram o mf easurement fso precten s(.Se ebelow fo erxpla¬ time, and from 1 1 to 1 3 during Waccamaw'-Caloosahatchee nati osynfmbols.) time. It is doubtful that these increases are a result of the temperature-diversity relationship ,as the Chipola is thought to be as warm as any of the later formations. Increase in diversity upward through the section appears to reflect an increasing diversification of the pectens as a group. Morphometry The morphometry of the species of pectens found in the Lee Creek Mine was studied by the use of all suitable valves. In some species the population sample amounts to 10 or fewer specimens, but in others as many as 90 specimens are available. Approximately 20 morphological characters were measured on each valve, although the number is variable among species because some lack certain characters, such a pslicae. The measuring devices and methods employed in this study are similar to those used by Waller (1969). The measurements of the exterior of the valve, except for con¬ vexity, were determined by placing the specimen on graph paper. The convexity of the valves was measured on a glass plate w ith the use of a large vernier caliper. The widths of the plicae and of the areas between the plicae were taken by vernier calipers, either internally or externally in various species. The number of plicae w as counted on the basis that the outermost plica must be reflected on the interior of the valve and he hounded externally on the disk-flank side by a distinct groove. The measurements of the resilial insertion and resilifer were taken through the ocular micrometer of th me icroscope. Measurements and Abbreviations.—A selection of NUMB E6R1 43 V Valve, left (S) or right (D) the Chesapecten lineage (Figure 23) and to a somewhat lesser W IWidth o finterspace sbetween plicae degree in the Argopecten eboreus stock ,with its many subspe¬ WP Width of plicae cies (Figure 1 1). Important Characters.— A small number of charac¬ Other aspects of ornamentation are also important in the ters were found important in characterizing and discrimi¬ pectens studied herein. These include significant differ¬ nating various species of pectens from the Miocene and ences in the number of costae on the plicae in the Chesapec¬ Pliocene strata in the Lee Creek Mine and environs. Al¬ ten group. The number of costae varies from 1 to 4 in C. though internal characteristics were found to be important coccymelus to as many as 20 in C. jeffersonius and C. madison¬ by Waller (1969), the musculature was not used in the ius. There also is a significant difference in the number of present study because of the difficulty in obtaining a large costae on the auricles with the number varying from as few enough population sample having these characters pre¬ as 6 in C. coccymelus to as many as 25 to 30 in C. jeffersonius served. In some species, the interior, and to a lesser extent and C m. adisonius. the exterior, is covered with an indurated matrix, which The arrangement of the internal lirae, which are char¬ requires considerable time for each specimen to be cleaned acteristic of Amusium, appears to be diagnostic of several by air abrasive methods. Also the air abrasion process erodes species. This character should be useful in specific identifi¬ enough of the weakly preserved muscle scars to make ac¬ cation as most of the specimens of Amusium are fragmentary. curate measurement of them difficult. In other groups that In Amusium the lirae vary from closely spaced pairs with do not have the indurated matrix, the state of preservation wider areas between pairs to essentially widely and uni¬ on the interior is not sufficient to allow careful study of the formly spaced lirae. muscle scar locations. The general morphological charac¬ teristics of the valve do yield important characterizations Acknowledgments and distinctions in all cases. In the Placopecten stock, attach¬ ment scars in the form of the resilial insertion are used as The author is indebted to Jack McLellan and Druid an important differentiating characteristic. Wilson for help in the collection of specimens from the Lee The valve shape among most pectens is similar, and in Creek Mine. Linda Larkie and Jeff Lund assisted in the only two groups in this study could species be differentiated measurement of specimens. The photographs of the speci¬ on the basis of valve shape. One is the Placopecten group, mens were taken by Robert McKinney. Jeff Lund prepared where the sample of P. clintonius clintonius from the Lee the illustrations and assisted in numerous other activities. Creek Mine has an oblique valve outline compared to the Warren Addicott, Thomas Waller, and Druid Wilson pro¬ Holocene sample of P magellanicus . The other is in the vided much appreciated critical reviews of the manuscript. Chesapecten group where C .nefrens differs from C .coccymelus Muriel Hunter kindly donated specimens from Florida to by having a longer valve in relation to the height. the USNM collections. The convexity of the valves varies greatly from genus to genus, but also varies within a species group as shown in Family Pectinidae Rafinesque, 1815 the Pecten humphreysi igroup (Figure 10) and the Argopecten eboreus stock (Figure 14). Genus Pecten Muller, 1776 The byssal notch is important as it may closely reflect anatomical changes. The byssal notch varies phylogeneti- Pecten mclellani, new species cally within the Chesapecten stock; the early members, such Plates I, 2, 13: Figure 2 as C. coccymelus and C. nefrens, have deep byssal notches; the next number, C. santamaria, has a notch of moderate Description. — Shell Outline: Shell medium to large in depth; the following species, C. middlesexensis, has a slightly size, with specimens having heights of 80 to 100 mm com¬ shallower notch; and the youngest members, C. jeffersonius mon in the population sample, and reaching a maximum and C. madisonius, have very shallow notches. This character height of 130 mm; slightly longer than high, with a maxi¬ also varies within other species groups or genera as shown mum length of slightly greater than 120 mm; right valve in Pecten humphreysi iand allies (Figure 9) and the Argopecten low to moderately convex with a maximum convexity of 17 eboreus stock (Figure 13). mm; left valve flat to slightly convex with a maximum The height and length of the auricles is a variable char¬ convexity of 9 mm; outline of disk equilateral, with almost acter within a species group ,as shown in Placopecten clinton¬ identical anterior and posterior half-diameters. ius (Figure 20). Auricles and Outer Ligament: Right anterior auricle with The plicae are among the most striking features in many a slightly convex surface; dorsal margin slightly dorsal to pecten groups, particularly in the Chesapecten group, where groove of outer ligament and folded; byssal notch very they are strongly developed. The number of plicae is a valid shallow with broad apex; byssal fasciole poorly developed; and useful characteristic. This chapter is especially useful in ctenolium observable on right valves. Left anterior auricle NUMB E6R1 45 Figur e7(to pleft).—Bivariat escatte dr iagram showin gth edifferenc ein the width o fthe interna lplica and groove between sample so fPecten humphreys (iCi alve rFtormatio nM, aryland a)n Pdm. clella n(Pi ung Roiver Formati oNno, rCtahrolina). Figur (8ebottom left).—Bivariat secatte driagram sho win gth deifference in the width o fthe interna lgroove compared to the heigh to fthe valve amon sgample oPsfecte hnumphrey s(iCi alve rFtormatio nM, arylan da)n Pd. mclella n(Pi ung Roiv eFrormatio nN,or tCharolina). Figur e9(right).—Bivariat escatte dr iagram showin gth edeepe bryssal notch in relation to the length o fthe anterio route rligamen tin a sample oPfecte hnumphreys (iCi alve rFtormatio nM, arylan dc)ompare td Pom. clel¬ la n(Pi ung Roive Frormatio nN,ort Charolina). Figu r1 e(0below).—Bivaria tsecatt edriagra mshowin tgh gereat ecronvex¬ ity o fthe righ tvalves compared to the heigh to fthe valve in a sample of Pecte hnumphrey s(iCi alve Frtormatio nM,arylan dc)ompare tPmdo.clellani LENG AOTNHFTERI OURT LEIRGAMENT (Pung Roiv eFrormatio nN,or tCharolina). mm LI HNEIAGRHT 46 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY with surface nearly planar to slightly convex; dorsal margin common in the latter. Figures 7 and 8 show the significantly slightly folded and nearly coincident with trace of outer greater width of the plicae on the right valves of P. hum¬ ligament; free margin slightly rounded with shallow byssal phreysii. (The measurements are taken internally as the sinus having a rounded apex. Posterior auricles similar in sharpness of the plicae is increased on the interior, giving size to anterior; dorsal margin slightly dorsal to groove of mor eaccurat emeasurements.) outer ligament and folded; free margin slightly convex, Although the byssal notch is shallow in both species, the especially near dorsal margin. Posterior and anterior outer position of the notch in relation to the anterior end of the ligaments generally about equal in length. outer ligament is different between the two species (Figure Exterior Shell Surface: Both valves with about 12 plicae; 9). In P. humphreysii the posterior end of the byssal notch is in early growth stages plicae defined from interspaces by 1 to 3 mm posterior to the anteriormost point of the outer low, moderately rounded sides until shell heights of approx¬ ligament. In P. mclellani the posterior end of the byssal imately 50 mm are reached, thereafter plicae becoming less notch is from 0.5 mm posterior to almost 1 mm anterior to strongly defined from interspaces with very broad, low the anteriormost end of the outer ligament. sides, until becoming obscure at margins of large valves; no The right valves of P. humphreysii have considerably secondary radial ornamentation on plicae or interspaces; greater convexity compared to those of P. mclellani as shown concentric lamellae well developed on left valves, less so on in Figure 10. right valves being primarily preserved on the disk flanks. As P. humphreysii is found in beds of the Pungo River Anterior and posterior auricles have approximately 8 radial Formation, below those in which P. mclellani occurs, and as costae, moderately developed on the initial 10 mm of the the two species have similar morphology, it is considered auricle, becoming obsolete beyond this point; concentric likely that P humphreysii is ancestral to P. mclellani. One lamellae well developed on auricles. Disk flanks of right important phylogenetic change between the two species is valves have 4 moderately developed radial costae on initial a decrease in the strength and width of the plicae in the 15 mm along with moderately developed concentric lamel¬ descendant species. Mature specimens of P. humphreysii do lae; left valves have smooth disk flanks except for well- show a decrease in the strength of the plicae in the later developed concentri clamellae. stages of the valve to a height and sharpness similar to that Interior Features: Resilial insertions slightly less than 1 ] A found in the early stages of P. mclellani. times as high as long, orientation ranging from perpendic¬ There is a general similarity in the shell shape, ornamen¬ ular to hinge line to slightly sloping either anteriorly or tation, both internal and external, and byssal characters posteriorly; single, strongly developed auricular denticle between P. mclellani and the later occurring Pecten holmesii both anteriorly and posteriorly; additional one or two costae Dali from the Waccamaw Formation in South Carolina. No found within the interior plicae. related species of an intermediate age is known, and the Discussion. —The only closely related species in the Mio¬ similarity may not reflect any relationship. An increase in cene strata of the Atlantic Coastal Plain is Pecten humphreysii convexity of the right valve of P. mclellani , however, along Conrad, which is found in slightly lower beds of the Pungo with a further reduction in the largely obscure plicae would River Formation in the Lee Creek Mine and in the Calvert give a form similar to that of P. holmesii. Formation in northernmost Virginia, Maryland, and New Pecten ochlockoneensis Mansfield from the Choctaw- Jersey. Pecten mclellani is distinguished from this species by hatchee Formation in Florida and/ 5 , smithi Olsson from the the ornamentation, position of the byssal notch relative to Yorktown Formation in Virginia differ from P. mclellani in the end of anterior outer ligament, and convexity of the having many more plicae on both valves and in being much righ vtalve. smaller in size. In addition, P ochlockoneensis has a more The number of plicae in P. mclellani is greater, ranging convex right valve. These two species are most similar to P. from 10 to 13 in number, while P. humphreysii has from 8 mclellani, but are doubtfully congeneric. to 10 (7 or 8 broad and prominent ones and two lateral Name. —The species is named in honor of Mr. Jack ones quite reduced in size, which are more prominent on McLellan of Iexasgulf Inc., who collected and donated the interior of the valve). Pecten humphreysii has much wider many specimens of pectens and other invertebrates from plicae on the right valve, with relatively narrower inter¬ the Lee Creek Mine. spaces and, correspondingly on the left valve, has relatively Types. —Holotype: right valve, USNM 218830. Figured narrow plicae with wide interspaces. The plicae on both paratypes: right valve, USNM 218828; right valve, USNM valves are quite pronounced with vertical sides in some 218829; left valve, USNM 218831; left valve, USNM specimens. P. mclellani has considerably narrower plicae on 218865; unfigured paratypes, USNM 218933, 362976, the right valve with the interspaces more nearly approach¬ 362977, 362978, and 362979. ing equal width with the plicae; on the left valve correspond¬ Stratigraphic, and Geographic Range.— The only ingly are wider plicae than in P humphreysii with narrower known occurrence of this species is in the upper part of the interspaces. The plicae are very slightly raised in compari¬ Pungo River Formation of early middle Miocene age in the son with P. humphreysii and do not have the vertical sides Lee Creek Mine in North Carolina. Well-preserved speci- NUMB E6R1 47 Tabl e1.—Measurement (si nmm o )arfepresentativ esampl eof Pect emnclella n ie,swpecies. width ratio increases slightly with ontogeny; right valvemoderately convex with maximum convexity of 26 mm; left valve planar to slightly convex in a few specimens; outline Character of disk equilateral with almost identical anterior and poste¬ rior half-diameters. Moderately developed disk gape both anteriorly and posteriorly, amounting to approximately a 4 to 5 mm gape in shells slightly greater than 100 mm in height. Auricles and Outer Ligament: Right anterior auricle with strongly convex surface, being raised as much as 6 mm above the plane of commissure in large valves; dorsal margin slightly dorsal to groove of outer ligament and slightly to moderately folded, increasing in degree toward anterior part; byssal notch very shallow with broad, rounded apex; byssal fasciole poorly developed; ctenolium of 3 teeth oc¬ casionally observed in very young stages. Left anterior auricle with strongly concave surface; dorsal margin slightly folded and nearly coincident with trace of outer ligament; free margin rounded with shallow byssal sinus having a rounded apex. Posterior auricles similar in size to anterior; surface planar to slightly convex; dorsal margin slightly mens are found in the upper 6-12 feet (1.8-3.7 m) (units dorsal to groove of outer ligament and slightly to moder¬ 4-7 of Gibson, 1967) of the Pungo River Formation, some ately folded; free margin straight to slightly convex. Poste¬ being found just an inch (2.5 cm) below the contact with rior and anterior outer ligaments generally about equal in the overlying Yorktown. This mine contains the only known length. Auricular gape relatively large both anteriorly and outcrop of this formation in North Carolina, the formation posteriorly, reaching 4 mm in the largest specimens. being limited to the subsurface except for this artificial Exterior Shell Surface: Both valves w'ith about 8 to 9 exposure. Strata of this age containing calcareous fossils do plicae. Right valves have broad plicae with relatively narrow not naturally crop out south of north central Virginia. interspaces, with ratio of width of plicae to width of inter¬ Measured Material.— Total specimens measured in¬ spaces of 20-30 to 1; in early growth plicae sharply defined clude: 3 right valves and 1 left valve from USGS 25743 and from interspaces with sides of plicae at angle of about 60 3 right valves and 1 left valve from USGS 25757. A popu¬ degrees to surface of valve; in later stages plicae of large lation sample from the Pungo River Formation at Lee Creek valves greater than 88 mm height, sides of plicae make low Mine, USGS 25743 and 25757, consisting of 8 specimens, angles of about 20 degrees to valve surface, giving low' and 6 right valves and 2 left valves, was measured. Measure¬ poorly defined plicae at the valve margins. Left valves have ments of a representative sample of 3 specimens are given narrow plicae with wide interspaces; plicae are sharply de¬ in Table 1 (USNM 218830, holotype, and USNM 218828, fined from interspaces in early stages, becoming less sharply both from USGS 25743; USNM 362976 from USGS defined at shell heights of about 80 mm. Secondary radial 25757). ornamentation of 4 to 10 costae of varying strengths and w idths on plicae of right valves; plicae on left valves rarely have 2 radial costae; no radial ornamentation in interspaces Pecten humphreysi ihumphreysi iConrad of either valve. Concentric lamellae moderately developed on right valves, both in interspaces and on plicae; lamellae Plate 3: figures 2-7; Plates 4, 5: figures 1, 2, 4; Plate 6: more strongly developed on interspaces and plicae of left figure s5 7, valves. Anterior and posterior auricles of right valves have Pecte nhumphreys iCi onrad 1,842:194 p, i2 .f:ig 2..—Mongin 1,959:297- 8 to 14 radial costae, w'hich vary in strength and spacing 299 p, i .25 :figs .la-b. and become obsolete about 25 mm from origin of growth; Vo lhaumphrey s(Ci onrad).—Whitfiel d1,894:32-3 4p ,4if.i:g s6.-9. both auricles of left valves have fewer costae, about 6 to 8, Pecte {nPecte nh)umphrey sCiionrad.—Glen n1,904:37 2p 9,i .8fi:g 1s.0-12— which have a more regular development but also become Schoonove r1,941:188-190 p, 2i.0 f:ig s1.-2. Pecte (nPecten h)umphrey sCionrad.—Tucke r1,936a:478-47 9p ,3if.i: g3.; obsolete about 25 mm from the origin of growth; concentric pi .4 :fig .10. lamellae well developed on all auricles. Disk flanks of right valves have 5 to 8 moderately developed radial costae, w hich Description.— Shell Outline: Shell medium to large in become obscure towards ventral margins, and well-devel¬ size, reaching a maximum height of 1 15 mm; slightly longer oped concentric lamellae; disk flanks of left valves have 3 than high, with a maximum length of 127 mm; length to to 5 weakly developed radial costae, which become obscure 48 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY towards ventral margins, and well-developed concentric is (1) an evolutionary development during this interval from lamellae. P. humphreysii to P. mclellani or (2) the environmental Interior Features: Resilial insertion elongated perpendic¬ changes between the beds are reflected in the occurrences ular to hinge line, being about twice as high as long; single of the two species. auricular denticle strongly developed both anteriorly and Stratigraphic and Geographic Range. — I his sub¬ posteriorly; single weakly developed costae w'ithin the inte¬ species is doubtfully present in the uppermost 3-6 feet (0.9- rio rplicae. 1.8 m) (units 6 and 7 of Gibson, 1967) of the Pungo River Discussion.— As mentioned under P mclellani, P. hum- Formation in the Lee Creek Mine, being represented by a phreysii differs from the former by having fewer plicae on single well-preserved individual not collected in place, but the right valve, which are wider and much more pro¬ possibly from unit 6 or 7 because of color and preservation. nounced, fewer, much narrower, and more pronounced In the lower part of the interbedded limestone and phos¬ plicae on the left valve, a deeper byssal notch, and a consid¬ phatic sand horizon (unit 4), however, specimens become erably greater convexity of the right valve as shown in more common and are quite common as molds and casts in Figure 10. The surface of the right anterior auricle in P. the phosphatic intervals below this (units 1-3). Many of the humphreysii is also more strongly convex. In addition, sec¬ phosphatic molds and casts are found in ore piles derived ondary radial ornamentation of costae on the plicae and from the more phosphatic beds that are void of original auricles of the right valve is better developed in P. hum¬ calcareou ms aterial. phreysii, both in coarseness and extent (Plate 3:figures 1, 2, This subspecies is found also in the lower and middle 4). The costae on the valves of P humphreysii are variable parts of the Calvert Formation in Maryland, being moder¬ in development; but the absence of costae on the plicae of ately common in bed 10 and lower beds. The typical form right valves in many larger specimens is probably a result and an additional subspecies ,P. humphreysii woolmani Heil- o wf ear. prin, have been described from outcrops of the Kirkwood Typical specimens of P humphreysii with approximately Formation and subsurface Miocene in New Jersey (Richards 8 or 9 broad, pronounced plicae are confined to the phos- and Harbison, 1942:186). An examination of the material phatic and dolomitic layers in the lower and middle part of in the USNM collections of the National Museum of Natural the Pungo River section and to the lowermost part of the History would place all specimens from New r Jersey into P. overlying interbedded phosphatic sand and limestone se¬ humphre wysoiiolmani. quence. On the other hand, P. mclellani is found only in the Banks and Hunter (1973:359) report P. humphreysii from upper sequence. Only one specimen of P. humphreysii was the Torreya Formation of early Miocene age from the obtained from possibly the upper part of the Pungo River northwestern part of Florida. Hunter kindly sent specimens section, that being a young individual found as float (Plate for examination, and three are illustrated in Plate 4: figures 3: Figure 5). The vertical change suggests that either there 4-6. The fragments of the left valves agree closely with Tabl e2 —. Measurement (si nmm o) arfepresentativ esampl eof P ehcutmenph rheuymsipi hreysii. Character NUMB E6R1 49 specimens of P. humphreysii humphreysii from Maryland as Shell Outline: Shell medium to large in size, with frag¬ does the largest right valve (Plate 4: figure 4). The other ments suggesting valve heights of greater than 100 mm; two right valves are of immature individuals and have more right valves moderately to strongly convex; left valve planar; sharply raised plicae with essentially vertical sides. A pro¬ outline of disk equilateral. nounced development of the plicae in the early stages with Auricles and Outer Ligament: Right anterior auricle with a general rounding of the edges of the plicae during ontog¬ essentially planar surface; dorsal margin slightly dorsal to eny is commonly found in larger specimens of P. humphreysii groove of outer ligament and folded; byssal notch shallow humphreysii from Maryland, and the Florida specimens are with broad, subrounded to angular apex; byssal fasciole placed in this subspecies. poorly developed. Left anterior auricle with slight to mod¬ The occurrence in Florida of P. humphreysii is by far the erately concave surface; dorsal margin nearly coincident farthest southern limit for this species. According to Banks with trace of outer ligament and slightly folded; free margin and Hunter (1973) the Torreya Formation is found in the slightly rounded with shallow byssal sinus having a sub¬ Gulf trough opening through the southeast Georgia embay- rounded apex. Posterior auricles similar in size to anterior; ment into the Atlantic Ocean. This opening would give a surfaces planar; dorsal margins nearly coincident with trace fairly direct migration route between the area of the Tor¬ of outer ligament and folded; free margins planar and reya Formation in Florida and areas farther north along slightly rounded. Posterior and anterior outer ligaments the Atlantic Coast, such as the Lee Creek Mine in North generally about equal in length. Carolina and Maryland. Exterior Shell Surface: Both valves with 7 or 8 plicae. The Torreya Formation is placed in the N5 or N6 plank¬ Right valves have broad plicae with relatively narrow inter¬ tonic zones of early Miocene age by Banks and Hunter spaces, with ratio of width of plicae to w idth of interspaces (1973). Bed 10 of the Calvert Formation at Plum Point, of 2.5-3 to 1; in early growth stages plicae sharply defined Maryland, and the upper part of the Pungo River Forma¬ with vertical to overhanging sides; in later stages plicae still tion in the Lee Creek Mine are placed in planktonic zones have almost vertical sides. Left valves have narrow plicae N8 or N9 by Gibson (1967; 1983b:360), making the Florida with w'ide interspaces; plicae have sharply defined sides specimens the oldest known of this species along the Atlantic throughout growth, although becoming less so in later and Gulf Coast. stages. Secondary radial ornamentation of 10 to 15 costae Grant and Gale (1931:222) and Fleming (1957:16) sug¬ of relatively uniform development on plicae of right valves; gested that the Pecten humphreysi igroup migrated ,probably plicae on left valves lack costae; occasional radial costae on during the Miocene or Pliocene from Maryland via Califor¬ interspaces of right valve (Plate 6: figure 1). Concentric nia to Japan where it persists as Pecten albicans Schroter. lamellae moderately developed on right valves, both in Measured Material. —A population sample from the interspaces and on plicae; lamellae more strongly developed Calvert Formation at the Basford Farm, USGS localities on interspaces and plicae of left valves. Anterior and pos¬ 23565 and 25744, and Howard Post Office, USGS locality terior auricles of right valves have about 12 to 18 weak 10278, consisting of 66 specimens, 24 right valves and 42 radial costae, which become obsolete about 30 mm from left valves, was measured. Measurements (in mm) of a origin of growth; auricles of left valves have fewer costae, representative sample of 8 specimens are given in Table 2 about 8 to 10, weakly developed, which quickly become (USNM 218838 is from USGS locality 23565, USNM obsolete; concentric lamellae w^ell developed on all auricles. 362980 through 362985 are from USGS locality 25744). Disk flanks of right valves have numerous fine radial costae, w hich become weaker anteriorly, but persist; as many as 25 costae on the posterior flank and about 10 slightly coarser costae on the anterior flank; both flanks have moderately Pecten humphreysii woolmani Heilprin developed concentric lamellae; left valves have about 5 fine costae on each flank and well-developed concentric lamel¬ Plate 3: figure 1, Plate 5: figure 3, Plate 6: figures 1-4, 6, lae. Plate 17 :figure 2 Interior Features: Resilial insertion elongated perpendic¬ Pect eHnumphrey vsi aiWr.oolma Hnieilpr i1n8,88:405. ular to hinge line, being about tw ice as high as long; single Pec tPe (enc the )unmphrey wsioolma nHieilprin.—Tucke 1r9, 36a:479-480, auricular denticle, moderately developed both anteriorly pi .4 :fig .11. an dposteriorly. Pect ehnumphrey wsioi olma Hnei ilprin.—Richar ad nsHdarbiso 1n9,42:186, pi .8 :figs .12-13 ,pi .9 :fig .2. Discussion. —Specimens of P. humphreysii occurring inNew Jersey were separated by Heilprin (1888:405) as “a Description. —Except for a few almost complete valves variety or subspecies” on the basis of having greater height of immature individuals, the samples are composed of frag¬ of the auricles, having a more distinct quadrangulation of mented specimens and a complete description and biometric the plicae on the convex valve, and having more prominent studies are not possible. striations on the plicae. Whitfield (1894:33) did not believe 50 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY the auricular characters differed between the two forms, Tabl e3.—Measurement (si nmm o )arfepresentativ esampl eof but he did not have a complete valve from New Jersey to Pe hcutemnphr weyosoiilmani. examine. Whitfield mentioned a considerably larger size for the New Jersey specimens, up to approximately 5 inches Character (12.7 cm) (based upon projections from incomplete valves), but specimens of such size from Maryland are in the USNM collections at the National Museum of Natural History. Tucker (1936a, pi. 4: fig. 11) figured a specimen she took as the neoholotype of P. humphreysii woolmani. It is a partial left valve and, along with relatively pronounced plicae, has a slight sulcus developed on the summit of the plicae. This sulcus was not observed on plicae on left valves of the numerous specimens in the USNM collections. An examination of the specimens of P. humphreysii wool¬ mani in the USNM collections, which number more than 50 fragmented valves, shows the prominent quadrangula- tion of the plicae mentioned by Heilprin (1888:405) to be a consistent feature of the right valves. Compared with the great majority of specimens from Maryland, the plicae on the right valves of the specimens from New'Jersey are much more sharply delineated from the interspaces ,having essen¬ tially vertical to overhanging sides on the plicae compared Genus Argopecten Monterosato, 1889 to sloping sides in the majority of the specimens from Maryland (Plate 3: figure 1). The specimens from New Argopecten eboreu s(Conrad) Jersey also have more sharply defined and higher plicae on Pect ebnore Cuosnr a1d8,33:341. the left valves. Other differences between the two subspecies Pec tPe (lnagioctenium e)bore uCsonrad.—Da 1li8, 98:7 4[ 9ipnart]. include the following: Pecten humphreysii woolmani has a Chla Pm l(aygsiocten eiub )more (uCsonrad).—Tucker-Rowlan 1d9,38:40-41, more convex right valve as deduced from the fragments of pi .3 .fig .12. larger valves; is lacking the convexity of the right anterior Chlam yA (sequipect ee )nbore (aConrad)—Gardne r1,944:36-3 7p , 7if.i:gs. auricle; generally has one or two fewer plicae, which are 1 ,5 ,6 ,8 [in part]).Argopecte enboreu (sConrad).—Walle 1r,969:59-6 1p 5,fi.i: g1.4. slightly broader; has weaker auricular denticles; and has more numerous radial costae developed on the plicae, au¬ Discussion.— This species is very common in the later ricles, and disk flanks in addition to the presence of an Cenozoic strata of the Atlantic Coastal Plain. Its oldest occasiona lcostae in the interspaces. occurrence is in the basal Yorktown Formation (= “Virginia Within a single population sample of P humphreysii hum¬ St. Marys” beds of Mansfield) of late Miocene age in Vir¬ phreysii from Maryland, a few valves fall within the range ginia, and it ranges into strata of Pleistocene age in Florida of ornamentation found in the specimens from New'Jersey. (Waller, 1969:60). Many morphologic variations are pres¬ They show a tendency toward quadrangulation of the plicae ent, and these have been made into a number of subspecific and development of more costae, but do not reach the taxa. Some of the subspecific characters are found only in development of the typical specimens. The geographic sep¬ a single group, but generally there is a complex mixture of aration of the areas of the two morphotypes, with probably the morphologic characters with some of the diagnostic 90 percent of the population sample in each area being subspecific characters being found in varying combinations. composed of one form, suggests that they are valid geo¬ The morphologic variation in this complex of subspecies graphic subspecies with some mixing in the area of overlap. led Gardner (1944:36) and Waller (1969:60) to place all the Stratigraphic and Geographic Range.— This sub¬ forms into a single species group without trying to apply species has been recorded only from the Kirkwood Forma¬ th esubspecifi cnames. tion of New Jersey, which is considered equivalent to the The earliest subspecies, A. eboreus urbannaensis (Mans¬ Calvert Formation in Maryland. field), from the low'ermost part of the Yorktow'n Formation Measured Material. —Total specimens measured in¬ in Virginia, is readily separable on morphologic criteria; clude 2 left valves (USNM 218847 and USNM 362986) but in the middle and upper parts of the Yorktown For¬ from USGS locality 2106, Kirkwood Formation, marl beds mation a group of names is available. These include A. near Jericho, Cumberland Company, New' Jersey. Their eboreus eboreus (Conrad, 1833), originally described from measurements are given in Table 3. the Yorktown Formation at Suffolk, Virginia, A. eboreus NUMB E6R1 51 darlingtonensis (Dali, 1898), described from the Duplin Marl spaces on the right valve, they are most commonly found near Darlington, South Carolina, A. eboreus watsonensis on the left valve. The squareness of the plicae varies from (Mansfield, 1936), described from the Ecphora zone of the very square to moderately rounded in samples from south¬ Jackson Bluff Formation in Florida, A. eboreus solarioides ern Florida, although the form with squared plicae is the (Heilprin, 1887), from the Caloosahatchee Marl of Florida, dominant one. This subspecies is found in the Caloosa¬ A. eboreus bertiensis (Mansfield, 1937), from the upper York- hatchee Formation in Florida, and also probably occurs in town beds at Mt. Gould Landing in North Carolina, and A. the Waccamaw Formation in North and South Carolina. eboreus senescens (Dali, 1898), described from the Wacca- A. eboreus senescens (Dali) was distinguished on the basis maw Formation in South Carolina. on having about 23 plicae, which become obscure in the Argopecten e. darlingtonensis (Dali) was characterized by later ontogenetic stages. This subspecies has been reported radial threads towards the margin of the disk (plate 9: figure from the Waccamaw Formation in North and South Caro¬ 1), along with 21 to 24 well-marked, angular plicae. How¬ lina. ever, in comparing the suite of type material of A. e. dar¬ Pecten yorkensis was described by Conrad (1867) from the lingtonensis with population samples from Suffolk, Virginia, Yorktown Formation at Yorktown, Virginia. A single left the type area for A. e. eboreus, the specimens from the valve (ANSP 38007) labeled Pecten yorkensis is in the collec¬ Suffolk area also have marginal threads on many specimens tions at the Academy of Natural Sciences at Philadelphia along with a similar number and character of the plicae. On and is chosen as the lectotype (Plate 9: figure 5). This these characteristics and a general overall morphologic sim¬ specimen closely matches the dimensions and number of ilarity, it would seem that these two subspecies, at least from plicae given in the original description. Although some their type areas, are synonymous. A variety of forms are workers (e.g., Mansfield, 1936:179, Tucker-Rowland, labeled A. e. darlingtonensis in the USNM collections, and 1938:38) have considered P. yorkensis to be a valid subspe¬ some of these undoubtedly belong to other members of the cies of Argopecten eboreus, this specimen appears to fall A. eboreus complex. Mansfield (1936:184) placed A. e. dar¬ within the range of variation of A. e. eboreus. lingtonensis in the phylogenetic development of A. eboreus There is considerable variation within the population as a time equivalent subspecies to A. eboreus eboreus, and samples of A. eboreus. Some populations include diagnostic leading tod. e. solarioides, but it is uncertain what specimens characteristics of several subspecies within a single sample. he was considering. The specimen illustrated by Mansfield The complex morphologic intergradation in the A. eboreus (1932, pi. 12: fig. l)asd. e. darlingtonensis from the Pliocene group needs a similar treatment to that given the A. gibbus of Florida appears to be related to A. e. solarioides. It would stock by Waller (1969). However, a stratigraphic succession be difficult, however, to place this specimen within the among some subspecies can be recognized. The earliest variation found in the type suite and other samples from subspecies, A. e. urbannaensis, is easily differentiated (there Sout hCarolina. is some question whether this is the basal stock or even a A. eboreus watsonensis (Mansfield) was distinguished by member of A. eboreus). This subspecies occurs in the basal having 18, nearly flat, nearly smooth plicae. Specimens part of the Yorktown Formation in Virginia (includes the belonging to this general morphologic type were reported upper part of the “Virginia St. Marys” beds of Mansfield). by Mansfield (1936) to occur in strata of Pliocene age in Occurring above this stratigraphically in the beds of zone 1 Florida and also in Mansfield’s zone 1 of the Yorktown of the Yorktown of Mansfield (1944) are the forms referred Formation in Virginia and North Carolina, and this mor¬ to here as A. eboreus aff. A. e. watsonensis. In the overlying phologic group could be identified in the present study. zone 2 of the Yorktown Formation is typical A. e. eboreus, A. eboreus bertiensis (Mansfield) differs in having a very which also would include at present A. e. darlingtonensis and convex left valve, and having an incised groove on the plicae A. e. yorkensis. Stratigraphically above, at least in the upper of both valves. In an examination of the type suite and beds of the Yorktown Formation along the Chowan River topotype material, the high convexity of the left valve is a in North Carolina, is A. e. bertiensis. This subspecies occurs constant characteristic, but the incised groove, although in the lowest beds exposed at Mt. Gould Landing; but the found on many, is not present on all the specimens. This strata 10 feet (3 m) higher in the section, which would be subspecies has been found up to now only at the type locality the uppermost part of the Yorktown Formation, have forms and at Colerain Landing, a short distance farther north on closely approaching A .e .solarioides ,along with an occasional the Chowan River. A. e. bertiensis. The highest group in the sequence is A. e. A. eboreus solarioides (Heilprin) was characterized as hav¬ solarioides, which occurs in the Waccamaw Formation in ing right valves with approximately 20 broad, squarish North and South Carolina and the Caloosahatchee Forma¬ plicae with narrow interspaces bearing radial striae. The tion in Florida, containing in a few places a component of number of striae vary in number from one to two in samples A. e. senescens as a part of the population structure. from different localities. Although striae occur in the inter¬ General characteristics noted during study and measure- SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY eAb.L oCerreee Mau eeAfsbkif.n.oere wusatsonensis NUMB E6R1 53 ment of the A. eboreus complex include the following: All preferred ratio, which may reflect the strongest way of forms have a slightly longer posterior half diameter than constructing the shell. The depth of the byssal notch be- anterior. Tbe convexity of the left valve is more variable comes shallower through the stratigraphic sequence de- within the species complex than that of the right valve, but scribed above of A. e. urbannaensis to A. e. solarioides (Figure the left valve is always more convex than the right. The 1 3), except for the reversal in the sample of A. e. aff. A. e. number of plicae varies from about 16 to 25 (Figure 11), solarioides from the Lee Creek Mine. but the width of the internal plicae is always greater than Lectotypes. —In addition to the lectotype designated the width of the adjacent groove. Moreover, regardless of for Argopecten eboreus yorkensis, ANSP 38007, left valve, the number of plicae and grooves, the ratio of the width of Yorktown Formation, Yorktown, Virginia, lectotypes also the internal plicae to the width of the internal groove is are selected for 3 additional taxa. essentially constant between forms (Figure 12), indicating a A lectotype is selected for A. eboreus darlingtonensis: right mm Figur e13.—Bivariat escatte dr iagram showin gth edifference si nth edept ho tfh ebyssa nl otc hi nrelation t oth leengt ho tfh vealv ie nvariou subgrouping os Afrgopecte neboreus. 54 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY valve, USNM 145432, from the Duplin Formation at USGS rounded; plicae wider than interspaces. Occasionally 3 or 4 2025 (Plate 9: figure 1). This is part of the type material, costae on the plicae and 1 or 2 in the interspaces, but most and is one of the cotypes selected by Tucker-Rowland specimens smooth. Concentric lamellae weakly developed (1938:42). The other cotype, a left valve, becomes a lecto- on interspaces and plicae of both valves. Right anterior paratype, USNM 218934. An additional lectoparatype is auricle has about 5 costae of moderate strength, left anterior illustrated (Plate 9: figure 4). about 8; both posterior auricles have about 10 weakly A lectotype is selected for A. eboreus urbannaensis: right developed costae; concentric lamellae moderately devel¬ valve, USNM 370829, from the basal Yorktown (“Virginia oped on auricles. Disk flanks have moderately developed St. Marys” bed) at USGS 3915 (Plate 11: figures 1, 3). This concentric lamellae and occasionally 2 or 3 weak costae. valve is one of the cotypes. The other cotype, a left valve, Interior Features: Resilial insertion about as long as high, USNM 218862 (Plate 11: figure 4), becomes a lectopara- orientation ranging from perpendicular to slightly posterior type. slant; single, weakly developed auricular denticle both an¬ A lectotype is selected for A. eboreus bertiensis : right valve, teriorly and posteriorly. USNM 496224, from the Yorktown Formation at USGS Discussion. —Mansfield (1936:188) characterized A. ebo¬ 1 1999. This valve is one of the cotypes (Mansfield, 1937, reus watsonensis as having “18 nearly flat, nearly smooth, fig. 1). The other cotype, a left valve, USNM 218935, moderately narrow ribs separated by spaces about as wide become s alectoparatype. as ribs’ and differing from A. e. eboreus “in having 5 to 8 fewer, more widely spaced ribs.” Argopecten eboreus aff .A .eboreus watsonensis The specimens from Lee Greek resemble the specimens (Mansfield), new combination of A. e. watsonensis from Florida in having the same number of plicae, a similar development of the plicae into more Plates 7 ,8 ,Plate 10: figure 4 squared profile in the higher, float specimens, and in having Pec t(eCnhlam yesb)ore wuastsonen Msisansfie 1ld9,36:188. the same width of the internal plicae and grooves. They differ in having a less convex right valve and a slightly Description. —Shell Outline: Shell of medium size, at¬ deeper byssal notch. Thus, for now, they will be treated as taining height of 80 mm; left valve of low to moderate having affinities to the Florida subspecies as they are gen¬ convexity and only slightly more convex than right valve. erally similar in morphologic characteristics and occur in a Outline of disk equilateral; disk flanks very low. Disk gapes similar stratigraphic interval. The specimens collected at narrow. Lee Greek support Mansfield’s statement (1936:184) that Auricles and Outer Ligament: Right anterior auricle with there is an additional form of A. eboreus between A. e. almost planar to slightly convex surface; dorsal margin urbannaensis from the lowermost part of the Yorktown slightly dorsal to groove of outer ligament, sharply folded Formation (“Virginia St. Marys’ beds of Mansfield) and the and thickened; folding of dorsal margin increases in amount typical A. e. eboreus of the younger Yorktown around Suf¬ away from origin of growth; byssal notch moderately shal¬ folk ,Virginia. low, with angular to rounded apex; byssal fasciole moder¬ The specimens from the Lee Greek Mine have 16 to 19 ately broad and slightly arched adjacent to suture and planar plicae, with most having 18 (Figure 11). Development of away from suture; ctenolium of 3 teeth in specimens up to the plicae ranges from relatively low and rounded, partic¬ 60 mm height, occasionally 1 tooth visible in specimens up ularly in the specimens collected in place in unit 3 of the to 80 mm height. Left anterior auricle with moderately Yorktown (Plate 7: figures 1, 4), to moderately high and concave surface; dorsal margin flat and nearly coincident squared, most common in the float specimens, which come with trace of outer ligament; free margin slightly rounded from higher units, probably units 4 and 5 (Plate 7: figure with shallow byssal sinus having a rounded apex. Posterior 2). I he left valve has an approximately median convexity auricles similar in size to anterior; right posterior has planar for the A. eboreus group, being more convex than A. e. to slightly convex surface with dorsal margin dorsal to urbannaensis and most convex in A. e. solarioides, but less groove of outer ligament and folded more strongly away convex than A. e. bertiensis (Figure 14). 'Fhe right valve is from origin of growth; left posterior auricle has concave moderately convex, being approximately the same as A. e. surface with dorsal margin nearly coincident with trace of urbannaensis and A. e. solarioides and more convex than A. outer ligament. Posterior and anterior ligaments generally e. bertiensis. The result lor the two valves is that the left about equa lin length. valve is only slightly more convex than the right, the closest Exterior Shell Surface: Number of plicae on valves varies to equal convexity of any sample of A. eboreus herein stud¬ from 16 to 19, with 18 being most common; plicae are low ied. 1 he type specimen of A. e. watsonensis and other spec¬ in early growth stages but sides are relatively sleep, with imens from Florida differ from the North Carolina speci¬ plicae remaining low in later stages but sides becoming mens in having a considerably more convex right valve. GROO VOEFWIDTH Figure 15.—Bivariate scatte rdiagram showing the difference sin the width o fthe interna gl roove in relatio nt oth eheigh o ttfh evalv ei nvariou subgrouping os Afrgopecte neboreus. 56 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY In the Lee Creek specimens the width of the internal naensis include 1 right valve and 5 left valves (USNM plicae is greater than the width of the internal groove 218862, 370829, 362991) from USGS 3915 and 11 right (Figure 12). The width of the internal groove compared to valves and 1 left valve (USNM 362990) from USGS 23468. the height of the valve is markedly different between the The specimens from USGS 3915 are from the lowermost Lee Creek specimens and those from Florida (Figure 15). part of the Yorktown Formation (= “Virginia St. Marys’” The Lee Creek specimens have approximately the same beds of Mansfield) on the river front at Urbanna, Middlesex length of the anterior and posterior auricles, but the height County, Virginia. Those from USGS 23468 are float from of the posterior auricles is greater than that of the anterior the beach of the Rappahannock River from Urbanna to the auricles. fish cannery. Measurements from a representative sample The specimens from the Lee Creek Mine can be differ¬ of 4 valves are given in Table 6. entiated from the stratigraphically lower A. e. urbannaensis Tota lspecimen smeasured o fArgopecten eboreu sbertiensis by a shallower byssal notch (Figure 13), fewer but better include 3 right valves and 4 left valves (USNM 218933, developed plicae (Figure 5), wider internal grooves (Figure 496224, 362992) from USGS 11999 and 20 right valves 15), a relatively shorter anterior auricle and lower posterior and 9 left valves (USNM 362993-362995) from USGS auricle, and a greater convexity of the right valve (Figure 25758. Those from USGS 11999 are from the Yorktown 14). Formation on the right bank of the Chowan River 0.75 Stratigraphic and Geographic Range. —Specimens mile (1.2 km) below Mt. Gould Landing, North Carolina. of A. eboreus aff. A. eboreus watsonensis were collected in Those from USGS 25758 are from the Yorktown Forma¬ place in unit 3 of the Yorktown Formation in the Lee Creek tion in a bluff on the west side of the Chowan River Mine, and in spoil material having an indurated matrix, approximately 0.5 mile (0.8 km) below' Mt. Gould Landing. which places the specimens as coming from units 4 and 5 of Measurements from a representative sample of 6 valves are the Yorktown Formation. Units 3-5 of the Yorktown For¬ given in Table 7. mation in the Lee Creek Mine belong to the lowest part of Mansfield’s zone 2 of the Yorktown. A. eboreus watsonensis w'as described by Mansfield Argopecten eboreus aff. A. eboreus solarioides (Heilprin),new combination (1936:188) from the Ecphora zone of the Jackson Bluff Formation in Florida, and was also listed from several Plate 9: figures 2 ,3; Plate 10: figures 1-3; Plate 11: figures 2 ,5; localities in zone 1 of the Yorktown Formation in Virginia. Plate 17 :figures 4 ,5 MacNeil (in Bergendahl, 1956:76) listed specimens from Pect seonlarioid Heesilpr 1in8,87:99. the Tamiami Formation in central Florida as having affini¬ ties to A. eboreus watsonensis, and additional closely related Description. —Shell Outline: Shell of medium to large specimens exist in the USNM collections. These specimens size, reaching maximum height of 1 1 8 mm; valves slightly are not typical A. eboreus watsonensis , but are closer to this longer than high with a maximum length of 125 mm. Right subspecies than to any other in the A. eboreus stock. The valve of low to moderate convexity, with a maximum con¬ age relationship of A. eboreus watsonensis and those speci¬ vexity of 22 mm; left valve only slightly more convex than mens having affinities with it is relatively close according to right. Out line of disk approximately equilateral, but slightly our current understanding of regional stratigraphy. They extended posteriorly in most specimens; disk flanks very occur in the Ecphora zone, upper lower and low'er middle low'. Disk gapes moderately broad, reaching 3 mm in larger parts of the Yorktown, and Tamiami formations. Except specimens. for A .eboreus urbannaensis ,this group is the earliest member Auricles and Outer Ligament: Right anterior auricle with of A. eboreus and looks like an ancestral form for the later planar to slightly concave surface; dorsal margin slightly subspecies. dorsal to groove of outer ligament, sharply folded and Measured Material.— Total specimens measured of thickened; folding and thickening of dorsal margin increase Argopecten eboreus aff .A .eboreus watsonensis include 6 right away from origin of growth; byssal notch moderately shal¬ valves and 3 left valves from USGS 25746 and 7 right valves low, with rounded to subangular apex; byssal fasciole mod¬ and 9 left valves from USGS 25338. A population sample erately broad and slightly convex; ctenolium of 1 or 2 teeth from the Lee Greek Mine, North Carolina, Yorktown for¬ common in smaller specimens, occasionally 1 tooth visible mation, USGS 25746 (in situ), and USGS 25338 (spoil in specimens up to 80 mm in height. Left anterior auricle bank), consisting of 13 right valves and 12 left valves, was with moderately concave surface; dorsal margin flat and measured. Measurements of a representative sample of 7 nearly coincident with trace of outer ligament; free margin valves are given in Fable 4. The measurements for the slightly rounded with shallow byssal sinus having a rounded holotype of Argopecten eboreus watsonensis ,USNM 371 139, apex. Posterior auricles similar in size to anterior; posterior from USGS 1 0962, Choctawatchee Marl, Watsons Landing, slightly higher than anterior; right posterior has planar to Liberty County, Florida, are given in Table 5. slightly convex surface with dorsal margin dorsal to groove Total specimens measured of Argopecten eboreus urban¬ of outer ligament and folded more strongly away from NUMB E6R1 57 1abl e4.—Measurement (si nmm o) arfepresentativ esampl eof Argopect ebnore ea uAbfsf.o. re wusatsonensis. Character Tabl e5 —. Measurement s(i nmm o) tfh eholotyp eo Af e.boreus Tab l7e.—Measurement (si nmm o )rafepresentativ seamp loef watsonensis. Argop eecbtoe bnrerutsiensis. Character Character Tabl e6.— Measurement (si nmm o) arfepresentativ esampl eof Argop ecbt oeurnrebuasnnaensis. Character origin of growth; left posterior auricle has slightly concave surface with dorsal margin coincident with trace of outer ligament. Posterior and anterior ligaments about equal in length. Moderate auricular gape both anteriorly and pos¬ teriorly. Exterior Shell Surface: Number of plicae on valves varies from 19 to 23, with 21 being most common; plicae are relatively sharply defined by steep sides in early growth stages and either remain so throughout or become broadly rounded and lower in later stages; width of plicae on right valves varies from about twice as wide as interspaces to approximately equal width. Right valves of forms with wider, squared plicae occasionally have 1 or 2 weak costae 58 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY on the plicae, but have moderately developed costae in the The majority of specimens from the Croatan Formation interspaces, consisting of 1 in the interspaces of the central at Lee Creek were collected in place over the thickness of part of the valve and 1 (or sometimes 2) in the interspaces this unit in the pit. They are grouped as a single population toward the anterior and posterior margins; the anterior sample with a few float specimens undoubtedly from the auricles have about 10 moderate to weak costae, and the same interval. The variation in characteristics of the plicae posterior, 10 to 12; concentric lamellae fair to poorly de¬ into several groupings could indicate a mixing of assem¬ veloped, mostly confined to interspaces. Left valve of forms blages of slightly different ages or environmental tolerances with squared plicae does not have costae on the plicae, but within the Croatan Formation. However, there does not usually have 1 well-developed median costa in the inter¬ seem to be any significant amount of time represented in spaces throughout the valve; the anterior auricles have 7 the upper shell bed in the area of collection and there is costae and the posterior 8 or 9; concentric lamellae well only a slight change upward in the environment of deposi¬ developed on interspaces and auricles. Right valves of forms tion. The preservation of the two extreme kinds is similar, with narrower, rounded plicae have 2 to 4 weakly developed and it is thought that they represent one variable popula¬ costae on the plicae and none in the interspaces; the anterior tion. Supporting this interpretation is the fact that samples auricles have 4 to 6 weak costae and the posterior about 9; of A. e. solarioides from the Caloosahatchee Formation in concentric lamellae well developed in interspaces and auri¬ Florida are dominated by specimens with squarish plicae, cles and also commonly on plicae. Left valves of forms with but there is considerable variation toward rounded plicae rounded plicae occasionally have 1 or 2 weak costae on the in some specimens. It appears that the populations of A. plicae and commonly have 1 and rarely 2 weak costae in eboreus at the time of deposition of the Caloosahatchee the interspaces; anterior and posterior auricles have about Formation and the upper bed at Lee Creek had a consid¬ 9 costae; concentric lamellae well developed on plicae, erable range of ornamentation. The two end groups seem interspaces, and auricles. Disk flanks of all valves have well- to be present in both areas, with a considerable proportion developed concentric lamellae and 2 to 4 weak costae. of forms with obsolete plicae in the Lee Creek beds of the Interior Features: Resilial insertion about as long as high, Croatan Formation and the Waccamaw Formation in South oriented perpendicular to hinge line except for slight pos¬ Carolina and fewer in Florida. A careful study of samples terior slant in some left valves; single, weak to moderate from both areas is needed to determine whether there is auricular denticle both anteriorly and posteriorly. sufficient difference in population structure to warrant rec¬ Discussion. —The population sample from the Lee ognition of two subspecies, but samples of this type are not Creek Mine differs from samples of A. eboreus solarioides available at the present time. Overall, the Croatan sample from the Caloosahatchee Formation of Florida by having a from Lee Creek is similar to A. e. solarioides in most char¬ much greater percentage of specimens with rounded rather acteristics, and it is considered to have closest affinities to than squared plicae, and by having a median costa in the th igsroup. interareas on both the right and left valves instead of just The Lee Creek specimens have radial costae in the inter¬ the left valve. There is a complex of forms in A. e. solarioides, spaces, a characteristic of A. e. solarioides. The interspace and this form certainly belongs to the lineage. ornamentation dominantly consists of a single costa, devel¬ The specimens from the upper shell bed (units 8 and 9) oped over most or all of the disk, and is found on both the in the Yorktown Formation in the Lee Creek Mine differ left and right valves. In some specimens the costae are only considerably from the specimens of A. eboreus aff. A. eboreus developed in the lateral interspaces, and in a few specimens watsonensis, which occur in the lower and middle part of the left valve has two costae in the lateral interspaces, a the formation. The specimens from the upper bed are characteristic of the specimens found in the Caloosahatchee larger in size, ranging to a height of 1 1 8 mm compared to Formation in Florida. The convexity of the left valve in the 79 mm for the largest specimen in the lower beds; the Lee Creek specimens is moderate among the A. eboreus number of plicae is greater, ranging from 19 to 23 with a group as a whole, with the right valve having a moderately mean of 2 1 compared to 16 to 19 for the lower specimens high convexity (Figure 14). The left valve is more convex (Figure 1 1), the byssal notch is shallower (Figure 13), and than the right, but this sample has the second closest simi¬ the width of the internal groove is narrower (Figure 15). larity in convexity between the two valves. The byssal notch The shape of the plicae in the sample from the upper bed is moderately shallow, being less than in A. e. watsonensis varies from individuals with broad and raised plicae with a and A .e .urbannaensis ,but slightly deeper than A .e .bertiensis square outline (Plate 11: figure 5), characteristic of A. e. (Figure 13). solarioides to those with relatively low and rounded plicae, Stratigraphic and Geographic Range. —This group which become poorly developed in the later portions of the is found in the Croatan Formation in the Lee Creek Mine, valve (Plate 9: figures 2, 3), similar to A. e. senescens, which and also in the uppermost part of the “Yorktown” at Mt. was described from the Waccamaw Formation in South Gould Landing along the Chowan River, North Carolina. Carolina. Measured Material. —Total specimens measured of NUMB E6R1 59 Tabl e8 —. Measurement s(i nmm o) arfepresentativ esampl eof Auricles and Outer Ligament: Right anterior auricle with Argopect enbore au eAfsbf..ore suoslarioides. a planar to slightly concave surface; dorsal margin nearly coincident with trace of outer ligament and slightly folded; byssal notch very shallow with broad, rounded apex; byssal Character fasciole poorly developed; no ctenolium observed. Left an¬ terior auricle with a planar to slightly concave surface; dorsal margin flat and nearly coincident with trace of outer ligament; free margin slightly rounded to straight with very shallow byssal sinus having a rounded apex. Posterior auri¬ cles similar in size to anterior; surfaces planar to slightly concave; dorsal margins nearly coincident with groove of outer ligament. Posterior and anterior outer ligaments gen¬ erally about equal in length. Exterior Shell Surface: Both valves with numerous radial costae, numbering about 9 to 10 per centimeter at heights of 100 mm; costae with steeply curved sides and rounded summits; costae narrower than interspaces; interspaces broadly U-shaped; on left valves additional costae during ontogeny added by intercalation; on right valves additional costae added both by intercalation and bifurcation; concen¬ tric lamellae poorly developed and usually worn; surface of well-preserved valves covered by small elongated pustules, which in some specimens become suggestive o fcamptonectes Argopecten eboreus aff. A. e. solarioides include 4 right valves microsculpture. Auricles have 10 to 12 costae with addi¬ and 3 left valves from USGS 25339 and 19 right valves and tional ones added by intercalation; concentric lamellae 7 left valves (USNM 362996-362998) from USGS 25364. weak ldyeveloped. Those from USGS 25339 are from spoil piles and those Interior Features: Resilial insertion slightly less than V/i from USGS 25364 from the upper shell bed, both at the times higher than long; orientation ranging from essentially Lee Creek Mine. Measurements from a representative sam¬ perpendicular to hinge line in most right valves to a gener¬ ple of 6 valves are given in Table 8. ally slightly posterior slope in most left valves; single, mod¬ erately developed auricular denticle, both anteriorly and posteriorly. Discussion. — Placopecten clintonius, a Miocene species, Genus Placopecten Verrill, 1897 was considered to be the ancestor of the living scallop, P. Placopecten clintonius clintonius (Say), magellanicus, by Dali (1898:726) and Gardner (1944:37) new combination because of the close morphologic similarity. The absence of any intermediate forms between these two species is prob¬ Plate 12: figures 2, 4, Plate 14: figures 1, 2, 5-7; Plate 15: ably due to the absence of fossiliferous cool water deposits figure s1 4, of latest Miocene and Pliocene age in the Atlantic Coastal Pecte nclintoniu sSay 1, 824:135 p, i9. f:ig 2. . Plain. Beds of this age in the Lee Creek Mine and surround¬ Pect (ePnlacopecte cnli)nton iSuasy.—D a1l8i,98:725. ing areas of North Carolina and southeastern Virginia are Chlam (yPslacopecte cnli)nton i(uSsay).—Tucker-Rovvla n1d9,38:52- 5p3i., of a considerably warmer character (Gibson, 1967; Hazel, 1 f:ig 1.1. 1971), which would seem to exclude the P. clintonius stock Chlam y(sPlacopecte nc)linton i(aSay).—Gardne 1r,944:3 7p 6,fii.:g s1.,4.— Mongin 1,959:299 p, i2.5 f:igs 2.a-d. on environmental grounds. P. clintonius is not found southof central North Carolina (the Lee Creek Mine) in the Description.— Shell Outline: Shell large in size, with Miocene, and specimens of the presumed living descendant, specimens having heights greater than 100 mm common, P magellanicus, have their southern boundary in the Atlan¬ and reaching a maximum height of at least 130 mm; length tic Ocean approximately at Cape Hatteras, North Carolina. of shell similar to height; left valve more convex than right; Fossiliferous cool-water deposits of latest Miocene and Pli¬ left valve moderately convex, reaching 25 mm in larger ocene age are not found on land in the more northern specimens; right valve low to moderately convex, reaching Atlantic Coastal Plain, but undoubtedly occur on the north¬ 14 mm; outline of disk moderately oblique posteriorly; ern continental shelf and there should contain the inter¬ moderate disk gape anteriorly and posteriorly, reaching 3 media tfeorms. mm. Dali (1898:726) mentioned the difficulties in separating 60 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY the two species, and used the following criteria: not exhibit as marked an obliquity of the valves. Th leatte [rP m. agellanicus c]an h,oweve rb, ae otnc deiscriminate dfrom Several of the other characters mentioned by Dali and th feoss bi ltyh sehorte hringe-lin eh,ighe aruricle sm, uc hnarrowe rresiliary others as distinguishing the two species were also studied. pit a, nd usually t,he smalle rand les scentra al dducto rsca ro fthe recent Dali (1898:726) and Tucker-Rowland (1938:53) mention shel l..As arul eth eradiating thread sin th efossil sar emarkedl ycoarser that a distinguishing character of P. magellanicus is the tha nthos eo tfh elivin gspecies. shorter hinge line as compared to P. clintonius clintonius. In The ornamentation, as represented by the radial costae, the populations studied, no difference in length of the hinge is generally considerably coarser in P clintonius, as men¬ line can be seen between the two species (Figure 18). If tioned by Dali (1898:726). Specimens of P. magellanicus anything, the larger specimens of P. magellanicus have a have finer costae ranging from 10 to 16 per centimeter at generally longer hinge line rather than shorter. 100 mm height. However, the more southern forms of P. Another differentiating character mentioned by Dali magellanicus have sufficiently coarse costae to overlap with (1898:726) is that the auricles are higher in P. magellanicus. some of the more finely costate P. clintonius. It appears that No significant difference was noted in this study (Figure some P. clintonius have coarser ornamentation than any P 19). Nevertheless the general trend is toward a slightly magellanicus ,and many P .magellanicus have finer ornamen¬ higher posterior auricle in P clintonius clintonius rather tation than any P. clintonius, but there is overlap in the tha ontherwise. middle of the sculptural range. Stratigraphic and Geographic Range. —This spe¬ A population study of the two species was made by cies occurs in abundance in the lower 2 to 3 feet (0.6 to 0.9 comparing/ 5 clintonius clintonius from the Lee Creek Mine m) of the Yorktown Formation in the Lee Creek Mine. (from spoil bank material derived from the lower two feet Mansfield (1929b: 1) used this species to name his lowest (61 cm) of the Yorktown Formation) with living P. magel¬ zone of the Yorktown Formation in Virginia, calling it zone lanicus taken on the Atlantic shelf east southeast of Long 1 or Pecten clintonius zone. P. clintonius clintonius is re¬ Island at 67 fathoms (USFC Sta. 2244). The comparison stricted to this zone, and is an excellent guide fossil in North involved those characters used by Dali and subsequent Carolina and Virginia. Another subspecies, P. clintonius authors as diagnostic between the two species, and some rappahannockensis (Mansfield) is found in the beds immedi¬ addition aolnes. ately underlying Mansfield's zone 1 of the “Yorktown” in As mentioned by Dali (1898:726), Tucker-Rowland North Carolina, and a slight distance below in several local¬ (1938:53), and Mongin (1959:299), the resilifer is consid¬ ities in Virginia. These beds were placed in the “Virginia erably broader in P. clintonius than in P. magellanicus. The St. Marys” beds by Mansfield (1944) but were included in gently sloping sides of the resilifer in many specimens make the Yorktown Formation by Gibson (1971). it difficult to obtain an accurate measurement. Because of Measured Material. —Total specimens measured of the possibility that the size and shape of the resilium is not Placopecten clintonius clintonius include 35 right valves and always closely correlated with the resilifer, measurements 27 left valves from USGS 25338, (USNM 362999-36300), were made on both for comparative purposes. The ratio of and 4 right valves and 7 left valves from USGS 25339 length to height of the resilial insertion differs between the (USNM 363001-363003). Both collections are from spoil two species, with P. clintonius having a considerably broader banks of the Yorktown Formation, Lee Creek Mine, North resilial insertion (Figure 16), supporting the views of Dali, Carolina, and include a total population sample of 39 right Tucker-Rowland, and Mongin. The resilifer also varies valves and 34 left valves. Measurements of a representative between the two species, with P. clintonius again having a sample of 8 valves are given in Table 9. broader one. While the correlation between height and length of the resilifer is lower than that of the resilial insertion, probably reflecting in large part the difficulty of Placopecten clintonius rappahannockensis (Mansfield), accurately measuring the resilifer because of the gently new combination sloping sides, this character could be used in species where the resilial insertion is not readily preservable. Plat 1e8 Valves of P clintonius clintonius from the Lee Creek beds Pect (eCnhlam ycsli)nton iruasppahannocken sMisansfie 1ld9,36:186-1 8p7i., are posteriorly oblique in shape, whereas valves of P. magel¬ 2 2f:ig s1.-3. lanicus are very slightly, if at all, oblique. This difference is Chla m(Pylascopec tcelin)to nraiupspahannocke (nMsiasnsfield).—Tucker- noted by comparing the anterior and posterior half-lengths Rowland ,1938:53-54 ,pi .3 :fig .6 ,pi .4 :fig .1. of the valves of the two species. As indicated in Figure 17, Description. — Shell Outline: Shell large in size, reach¬ P clintonius clintonius has a considerably larger posterior ing heights of 1 30 mm; length of shell is similar to or slightly half-length, whereas P. magellanicus has nearly equal pos¬ greater than the height; left valve more convex than right; terior and anterior half-lengths. Other specimens of P lefi valve moderately convex, reaching 19 mm in larger clintonius clintonius from various localities in Virginia do specimens; right valve of low convexity, reaching 13 mm in NUMB E6R1 61 mm HEIG H ORTFESILI AINLSERTION Figur e16 —. Bivariat escatte rdiagram showin gth edifference si nth esiz eo tfh eresilia ilnsertio namong sample osfubspecie osPflacopecte cnlintoniu (sYorktow Fnormatio nN,ort Charolin aa)n Pdm. agellanicus (Holocen Ne,e Ewnglan sdhelf). Tab l9e.—Measurement (si nmm o )rafepresentativ seamp loef Placope cltiennto cnlinutsonius. USNM Characte 3r62999 LENGT HALNFTERIOR POSTE HRLEIAONLRGF TH Figur e17.—Bivariat escatte driagram showin gth edifferenc ei nth eshape othf vealv aemon vgariou ssubgrouping oPsflacopecten. 62 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY larger specimens; outline of disk equilateral with essentially compared to P. magellanicus (Figure 16). identical anterior and posterior half-diameters; disk gape Emmons (1858:280) named Pecten princepoides from the moderately broad anteriorly and posteriorly. Miocene strata along the Meherrin River near Murfrees¬ Auricles and Outer Ligament: Right anterior auricle with boro, North Carolina. From the type figure and subsequent a planar to slightly concave surface; dorsal margin nearly collecting in the type area, it is clear that this taxon belongs coincident with trace of outer ligament and slightly folded; to Placopecten clintonius as Dali (1898:726) noted. Of which byssal notch very shallow with broadly rounded apex; byssal subspecies it is a synonym is a more difficult problem as fasciole poorly developed; no ctenolium observed. Left an¬ both subspecies are found in this area, in places within a terior auricle with a planar to slightly convex surface; dorsal foot of each other stratigraphically. The type figure (Em¬ margin nearly coincident with trace of outer ligament and mons, 1858, fig. 198) seems to be of a finely striate form slightly folded; free margin slightly rounded to straight with like/ 5 ,clintonius rappahannockensis ,bu tthe description (Em¬ a very shallow byssal sinus having a rounded apex. Posterior mons, 1858:280) mentions that the radiating striae are auricles similar in height to anterior and have essentially "coarse,” which would seem better to fit P clintonius clin¬ planar surfaces. Anterior outer ligament longer than pos¬ tonius. The description also mentions that the ears are terior. Moderate auricular gape. unequal, which would be indicative of P. clintonius rappa¬ Exterior Shell Surface: Both valves with numerous radial hannockensis , as would be the size which has a length of 5% costae, numbering about 11 to 15 per centimeter at height inches (13.3 cm). A final determination will have to be made of 100 mm; costae low, with steep sides and flat, broad from whatever type material can be found. summits; costae equal in width to slightly narrower than Stratigraphic and Geographical Range.— This interspace; interspaces broadly U-shaped; on left valves subspecies occurs in the upper part of the “Virginia St. additional costae during ontogeny added by intercalation Marys” beds of Mansfield (1944:6), also called zone 2 or and bifurcation; on right valves additional costae added Crassatellites meridionalis zone .These strata were reassigned largely by bifurcation; concentric lamellae poorly developed by Gibson (1971) to the lowermost part of the Yorktown and usually worn. Auricles have 5 to 10 weakly developed Formation as the initial part of the Yorktown depositional costae; concentric lamellae poorly developed. cycle in the Virginia-northern North Carolina area. The Interior Features: Resilial insertion slightly higher than subspecies is found in beds of this age along the Rappahan¬ long; orientation generally with a slight posterior slant in nock and James rivers in Virginia and the Meherrin River both valves; single, moderately developed auricular denticle in northernmost North Carolina, and occurs immediately both anteriorly and posteriorly. or closely below the strata of Mansfield’s zone 1 of the Discussion. —This subspecies differs from P. clintonius “Yorktown,” the P. clintonius clintonius zone. clintonius in characteristics of the radial ornamentation. The Measured Material.— Total specimens measured of costae in P. clintonius rappahannockensis are more numer¬ Placopecten clintonius rappahannockensis include 5 right ous, numbering from 11 to 15 per centimeter, are lower valves and 4 left valves (USNM 218878, 218879, 363004) and wider with broadly rounded to flattened summits, and from USGS 3924, one right valve from USGS 8179, and 5 the interspaces are relatively narrow and shallow. In com¬ right valves and 4 left valves (USNM 363005-363007) from parison, the costae on P clintonius clintonius range from USGS 25747. All are from the lowermost part of the approximately 5 to 10 per centimeter, are higher and Yorktown Formation: USGS 3924 from bluff at “Jones narrower with subangular to rounded summits, and the Point” on the Rappahannock River about 21 km north of interspaces are relatively deep and broad. Urbana, Virginia; USGS 8179 from the beach about 0.8 As mentioned by Mansfield (1936:187), the hinge line of km downstream from “Jones Point”; USGS 25747 from P clintonius rappahannockensis is longer, although this is bluff on Meherrin River 4.8 km above Highway 158 bridge. mostly characteristic of immature specimens (Figure 18). Measurements from a representative sample of 9 valves are The height of the auricles in the two subspecies is similar given in Table 10. (Figure 19), but P. clintonius rappahannockensis has a longer anterior auricle in relation to shell length (Figure 20) and a Placopecten sp. aff. P. magellanicus (Gmelin), longer anterior auricle than posterior. P. clintonius clintonius new combination has auricles approximately equal in length. Hie valves of P clintonius rappahannockensis are essen¬ Plate 16: figure 1 ,Plate 17: figure 3 tially equilateral, and differ from the Lee Creek sample of Ostr meaagellan iGcame l1in7,91:3317. P clintonius clintonius in which the valves are sharply not equilateral (Figure 17). Other population samples of P. Description. — Shell Outline: Shell medium in size, clintonius clintonius from Virginia, however, more closely height of 88 mm; length slightly longer than height; right approach being equilateral. The resilial insertion has a valve with low convexity of 9 mm; outline of disk essentially relatively great length in both subspecies of P. clintonius equilateral with a slightly longer posterior half-length. LENGTH Figur e1 —8. Bivariat escatte rdiagram showin gth esimilarit yi nth elengt ho tfh ehing elin eamon gvarious subgrou Ppl iaoncfgospecten. mm L IHNEIAGRHT mm LENGTH 64 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY Tab l1e0.—Measurement (si nmm o )rafepresentativ seamp loef Placop celicnt treoannpipuashannockensis. Character Auricles and Outer Ligament: Right anterior auricle with shell; hut the crucial information as to the exact strati¬ a planar surface; dorsal margin nearly coincident with trace graphic occurrence in the Yorktown Formation is lacking. of outer ligament and slightly folded; byssal notch very The cementation of part of an echinoid test onto the shell shallow with broadly rounded apex; byssal fasciole poorly is a strong indication that the specimen came from unit 2 developed; no ctenolium observed. Right posterior auricle of Gibson (1967). From a phylogenetic viewpoint, the spec¬ with planar surface; dorsal margin nearly coincident with imen should come from somewhere above the basal beds of trace of outer ligament and folded; free margin slightly the Yorktown, which contain the supposed ancestor, typical curved. Posterior auricle similar in height to anterior. An¬ P. clintonius, and if it is from unit 2 this would be true. terior outer ligament longer than posterior. Because there is only the one specimen, and particularly Exterior Shell Surface: Right valve with numerous radial because the precise stratigraphic position is uncertain, the costae, about 1 6 to 18 per centimeter; costae are low and specimen will not be placed more definitely taxonomically broad, with gently sloping sides; costae wider than inter¬ until additional valves with stratigraphic information are spaces; interspaces shallow and narrow; concentric lamellae found. The specimen has closer proximity to P. magellanicus poorly developed. Auricles with about 10 weakly developed morphologically, although it is presumably very close to P. costae ;concentric lamellae moderately developed. clintoniu sstratigraphically. Interior Features: Resilial insertion about as long as high, T he shape of the single right valve of Placopecten sp. aff. oriented perpendicular to hinge line; single, moderately P. magellanicus is similar to that of the modern P. magellan¬ developed auricular denticle both anteriorly and poste¬ icus in being equilateral with a fairly equal anterior and riorly. posterior half-length (Figure 17). This contrasts with the Discussion. — Placopecten clintonius from the Yorktown moderately oblique shape of the disk in a population of P. Formation of the Atlantic Coastal Plain has been considered clintonius clintonius from the Lee Creek Mine. the ancestral form of the living I\ magellanicus of the North I he ornamentation on the disk of Placopecten sp. aff. P. Atlantic Ocean (Dali, 1898:726). However, no forms tran¬ magellanicus consists of very fine radial costae. The strength sitional in morphology or age between the two species have of the costae is considerably less than that found in P. been found in the younger Cenozoic strata of the Atlantic clintonius, especially in the population from the mine, which Coastal Plain. A single right valve found in the Lee Creek has moderate to coarse radial ornamentation. The single Mine appears to be an intermediate form between the two specimen from the mine has costae that fall about midway species in that lineage. The specimen was collected by Jack in the range of variability of P. magellanicus, not being as McLellan from spoil banks in the Lee Creek Mine. It was sharply defined as in the coarser forms, but not being so determined to be from the Yorktown Formation on the flat as to be essentially smooth as in the more Finely orna¬ basis of the type of sediment adhering to small cracks in the mente edxamples. NUMB E6R1 65 T he auricles of Placopecten sp. aff. P. magellanicus are clintonius clintonius cannot be dismissed entirely, but as little different from those of both P clintonius and P. magellani¬ variation toward this form is observed in the hundreds of cus, although they are more similar to the latter. In com¬ valves examined from the Lee Creek Mine and other sec¬ parison to P. clintonius clintonius, the auricles in the single tions in the Atlantic Coastal Plain, it seems unlikely. specimen of Placopecten sp .aff .P .magellanicus have consid¬ Measured Material.— The measurements of the spec¬ erably finer costae. The posterior auricle has an essentially imen of Placopecten sp. aff. P magellanicus, USNM 218873, straight free margin perpendicular to hinge line, whereas from USGS 25743; spoil piles, Lee Creek Mine, North in P. clintonius this margin has a strong posterior slant away Carolina, are given in Table 11. from the hinge line. In the specimen of Placopecten sp. aff. P. magellanicus the anterior end of the anterior outer liga¬ Genus Chlamys Roding, 1798 ment is about the same distance from the origin of growth as is the innermost part of the byssal notch. In P. clintonius Chlamys decemnaria (Conrad) the bysall notch is more anterior than the anteriormost end of the ligament. The hinge line of Placopecten sp. aff. P. Plate 15 :figures 2 ,3 ,5-7 ,Plate 16 :figures 3-5 ;Plates 19 ,20 magellanicus is longer than most specimens of P. clintonius Pecte ndecemnariu Csonrad 1,834:151 1;840:49 p, 2i.4 f:ig 2.. clintonius (Figure 18). Although there are close similarities Pecte nvirginianu sConrad 1,840:46 p, i2.1 f:ig 1.0. in most characteristics of the auricles between the popula¬ Pecte ndispalatu sConrad 1,845:74 p, i4.2 f:ig 3.. tion of P. magellanicus and the specimen of Placopecten sp. Pec t(ePnlacopect evnir)ginian Cuosnrad.—D 1a8li9, 8:727. aff. P. magellanicus (Figure 19), the latter has longer auricles Pec t(eCnhlam dyse)cemnar Ciuosnrad.—D 1a8li9, 8:741. than most specimens of P magellanicus. (See Plate 16: Chlam (Pylsacopect veinrg) inian (uCmonrad).—Tuc k1e9r3,4:617.Chlam y(sChlamy sd)ecemnariu (sConrad).—Rowlan d1,936 b1:00 9p 8,i.: figures 1 and 2 where the similar-sized valve of P. magellan¬ fi g5s-6. . icus has considerably shorter auricles.) Chla m(Pylascopec tveirng)inia (nCuosnrad).—Tucker-Rowl a1n9d3,8:55-56, The resilial insertion of Placopecten sp. aff. P. magellanicus pi .4 :fig .22 ,pi .5 :fig .14. is relatively long in relation to its height, being similar to Chlamy dsecemnar i(aConrad).—Gardne r1,944:31-3 2p ,5if.i:g s1.- 26,.7. the shape of P. clintonius but significantly wider than that Chlam y(Pslacopecte nvi)rginian (aConrad).—Gardne 1r9, 44:38-3 p 94i,:.fi g3. of P. magellanicus. No absolute measurements are given for the resilial insertion, as it is fractured and separated. Description.— Shell Outline: Shell of medium size, at¬ Placopecten sp. aff. P. magellanicus is close to P magellan¬ taining height of 78 mm; both valves of low to moderate icus in many characteristics, and appears to be well along in convexity, with left valve of equal to slightly greater con¬ the phylogenetic sequence from P. clintonius clintonius to vexity than right. Outline of disk equilateral; height of valve that species. Unfortunately, without knowing how far above similar to length; disk flanks low. Narrow disk gape anter¬ the basal Yorktown beds (containing P. clintonius clintonius ) iorly ,none posteriorly. the specimen occurred, the rapidity of this transition cannot Auricles and Outer Ligament: Right anterior auricle with be determined. As mentioned, the nature of the small planar surface; dorsal margin slightly dorsal to groove of amount of sediment in crevices on the specimen and the outer ligament and strongly folded; byssal notch moderately echinoid fragment cemented to the shell suggest that the deep with broadly to moderately rounded apex; byssal specimen came from the upper lower part of the Yorktown fasciole moderately broad and planar; ctenolium with 3 to or lower middle part of the Yorktown (upper part of unit 2 4 teeth well developed throughout. Left anterior auricle to lower part of unit 5, most probably unit 2), indicating a with planar surface; dorsal margin flat and coincident with rapid phylogenetic change. The possibility that the single trace of outer ligament; free margin straight and essentially specimen is an extreme variant within the population of P. 90 degrees to hinge line. Posterior auricles much smaller than anterior; surfaces planar; free margin straight, slanted Tabl e11.—Measurement (si nmm o) tfh especime nof posteriorly. Anterior outer ligament almost twice as long as Placopect es nap mPf.f..agellanicus. posterior. Exterior Shell Surface: Radial ornamentation on right valve less strongly developed than on left valve; radial Character ornamentation varies greatly in development; disk orna¬ mentation ranges from very low, broad costae separated by narrow grooves, numbering about 16 to 18 costae per centimeter, to strongly developed plicae, numbering 10 to 12 per disk; costae increase in number by bifurcation, may be unequal strength. Right valves have plicae broader than interspaces; plicae vary in development from low with broadly rounded sides to low with almost vertical sides; 66 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY interspaces contain 3 costae. Left valves have narrow plicae occur commonly in the coarser stages of the plicae (figures with interspaces 3 to 4 times as wide; plicae vary in shape 10, 13). A similar increase in the development of the plicae from very low and rounded to moderately high and sharply and other ornamentation is observable on the left valves defined; costae not present on the plicae; as many as 12 (Plate 20). Because the costae and/or plicae are coarser on costae in the interspaces. Concentric lamellae developed the left valve than on the right, specimens with a finely only on strongly plicate right valves, but strongly developed costate right valve usually have moderately strongly sculp¬ on all plicate left valves. Right anterior auricles have 6 to 8 tured left valves. Therefore, finely sculptured left valves costae, low, rounded, and broad with narrow grooves; right are not common, but do occur (figure 2). The costae in¬ posterior have 6 to 20 low and narrow costae, more weakly crease in coarseness (figure 3), and then valves occur with developed than on anterior; auricles on left valve have 10 raised areas or plicae composed of two or three costae to 20 costae, with generally more on the anterior than formed by bifurcation of an earlier raised single one (figure posterior; there is no increase in strength of the costae on 5). The plicae become stronger, and along with them the the auricles with increasing strength of the costae and plicae intervening costae (figures 6, 7), with the development on the disk. Concentric lamellae poorly to moderately de¬ commonly of coarse concentric lamellae as on the right veloped on auricles of right valves, more strongly developed valve (figure 8). The extreme stage consists of three to five on auricles of left valves. strong plicae along with a number of weaker plicae in Interior Features: Resilial insertion about 1 x /i times as varying stages of development, reflecting the coarsening of high as long, oriented perpendicular to hinge line; single, the costae between the plicae, commonly those formed by weakly developed auricular denticle both anteriorly and bifurcation from the original strong one (figure 9). In this posteriorly. variation, i.e., Pecten dispalatus Conrad, both the stronger Discussion.— Samples of more than 300 specimens of and weaker plicae have coarse concentric lamellae. Pecten decemnarius and Pecten virginianus from the Lee Although the ornamentation is intergradational between Creek Mine show the complete intergradation of these the two nominal species, a check of other possibly significant previously separated species. These two forms are only morphological characters was made to see if they also moderately common in most localities and, although people showed overlap. Specimens were divided into three groups have noted the co-occurrence and similarities between on the basis of the strength of the ornamentation. These them, heretofore they have not been considered as belong¬ groups included the following three forms: (1) those with ing to a single variable species. For example, Mansfield fine to moderate costae, without plicae, i.e., typical Pecten (1936:178) noted that “ Pecten decemnarius Conrad and Pec¬ virginianus ; (2) those with moderately developed costae and ten virginianus Conrad are closely related and usually occur the incipient to moderate appearance of plicae, i.e., Pecten together.” In the same paper, Mansfield considered both decemnarius ; and (3) those forms with well-developed plicae species questionably to have evolved from Placopecten clin- and moderate to coarse costae along with concentric lamel¬ tonius. A population sample was composed of specimens lae ,i.e. ,typica lPecten decemnarius. occurring together on the spoil piles in a similar matrix, A comparison among the three morphologic groups was coming from the indurated silty sand in the lower part of made on the basis of external shell morphology, including unit 5. Chlamys decemnaria and rotten specimens of Turri- features of the disk, auricles, and byssal notch. None of the tella are about the only fossils present. comparisons indicates any difference among the three The presence of articulated specimens in the Lee Creek groups. Whether the characters used have a very high material shows the variation in the strength of the orna¬ correlation (Figure 21) or only a moderate correlation mentation on the two valves of an individual specimen. (Figure 22), the three groups show no significant differ¬ Regardless of whether the general development of the ences. Characteristics of the byssal notch, which have ornamentation is strong or weak, the right valve has consid¬ proven important in other species and genera, show that erably weaker development than the left (Plate 15: figures although the relatively deep byssal notch is a variable char¬ 2, 3, 6, 7; Plate 16: figures 4, 5). Within the large sample, acter within each group, it is similar among the three groups it is possible to demonstrate an intergrading sequence of (f igure 22). I he considerably greater length of the anterior ornamentation from fine radial costae to coarse plications auricle in comparison to the posterior auricle also is consist¬ with coarse concentric lamellae (Plates 1 9, 20). On the right ent among the three groups (Figure 21). Because of the valves (Plate 19) the ornamentation exhibits wide variation, indurated matrix on the specimens, only external characters ranging from fine costae (figure 1) to moderate costae on a wer uesed. slightly undulating surface marked by more conspicuous 1 he absence of significant differences in any of the stud¬ grooves (figure 2), to moderately coarse costae with the ied characters among the three groups reinforces the con¬ undulations and grooves developing into plicae (figures 3- clusion that the range in ornamentation is just a variable 5), and then to increasingly better developed plicae with characteristic of a single species. This wide range of orna¬ coarser costae (figures 6-13). Coarse concentric lamellae mentation is greater than in most species of pectens. As NUMB E6R1 67 mm POS AT LUOE NBERFONYISOCTGSCLRT AEOHLDFEPTH LENGT O AHFNTERIO ARURICLE LENG T ODHFISK 68 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY both the finer and more coarsely ornamented forms are Tabl e12 —. Measurement s(i nmm o) afrepresentativ esampl eof generally found in most localities, it appears that the wide smoo ftohr m Cohsf lam dysecemnaria. range of ornamentation is a common genetic characteristic throughout the time range of the species. It also appears that as far as can be determined no phylogenetic or geo¬ Character graphic trends toward finer or coarser plicae are present in the North Carolina-Virginia area. A wide variety of species have been placed in Chlamys, including the more recent placements of “ Pecten" decemnar¬ ius. Although the ornament pattern in “ Pecten' decemnarius is within the range of the type-species of Chlamys and other closely related species, it differs in not having the elongated shape of the disk characteristic of Chlamys islandicus, the type-species. Until a thorough reclassification of the Pectin- idae is available, “ Pecten decemnarius is placed in the genus Chlamys. “Pecten virginianus generally has been placed in the then subgenus Placopecten (Dali, 1898:727; Tucker- Rowland, 1934:617; 1938:55; Gardner, 1944:38), although these workers noted that “ Pecten ’ virginianus and Placopec¬ ten clintonius differ by the former having a much deeper Tabl e 13 —. Measurement s(i nmm o) afrepresentativ esampl eofintermedia ftoer Cmohfslam dyescemnaria. byssal notch and a strongly developed ctenolium. These two species were placed in the then subgenus Placopecten because of a general similarity in the shape and convexity Character of the two valves and their fine radial ornamentation. Dif¬ ferences in the byssal notch, however, and the intergrada¬ tion with coarser radial ornamentation including plicae in the “P.” virginianus and “P. ” decemnarius suite, make this placement questionable. The transition between “P.” virgi¬ nianus (usually placed in the subgenus Placopecten) and “P. ” decemnarius (usually placed in the subgenus Chlamys) does indicate that there may be a close relationship between the two groups, here regarded as genera. Stratigraphic and Geographic Range. —This spe¬ cies occurs in units 3 to 5 of Gibson (1967) in the Yorktown Formation at the Lee Creek Mine and is fairly common in this interval. The species previously has been reported in the Yorktown Formation from the Pamunkey River in Virginia southward to Greenville, North Carolina (Gardner, 1abl e14 —. Measurement s(i nmm o) afrepresentativ esampl eof 1944:32). Dali (1898:741) also reported it from the Ashley coar sfoerm Cohsf lam dysecemnaria. Ri ver phosphate rock in South Carolina, but the specimen is only a small fragment of an external mold and cannot be placed with certainty. This species usually occurs strati- Character graphically closely above the range of Placopecten clintonius, which is the common guide species to the lower part of zone 1 of Mansfield (1944). Chlamys decemnaria is recorded by Mansfield (1936:178) in the lower part of his zone 2, but he considered its occurrence doubtful in zone 1. It is possi¬ ble that some of the occurrences of this species, such as the lower part of the range in the Lee Creek Mine, should be placed in the upper part of zone 1 of the Yorktown, but the sparsity of the associated fauna limits this determination. As of this time, therefore, the known range of the species is the lower part of Mansfield’s zone 2 of the Yorktown Formation. Measured Material. —Total specimens measured of BN 4 4 NUMB E6R1 69 Chlamys decemnaria include 88 right valves (USNM 218890, ing a scabrous appearance. Disk flanks steep and covered 363008-363016) from USGS 25338, spoil banks of the with numerou scostae. Yorktovvn Formation, Lee Creek Mine, North Carolina. Inferior Features: Resilial insertion about twice as high Measurements from representative samples showing radial as long; oriented with a slight to moderate posterior slope; ornamentation relatively smooth (4 valves), intermediate (3 single auricular denticle of weak to moderate development valves), and coarse (3 valves) are given in Tables 12-14. both anteriorly and posteriorly. Discussion. —This species is one of the most abundant mollusks in the lower part of the Yorktown Formation in Genus Chesapecten Ward and Blackwelder, 1975 the Lee Creek Mine. The Chesapecten group exhibits a great amount of morphologic change during its phylogeny, mak¬ Chesapecten jeffersonius jeffersonius (Say) ing it valuable for biostratigraphy, and C. jeffersonius has Plate 21: figures 1-6, Plate 22: figures 4-6, Plate 23: several forms that are distinctive for the lower and middle figure s4 5, parts of the Yorktown Formation. The morphologic trends within the C. jeffersonius lineage are being studied by the Pecte nJeffersoniu sSay 1,824:133 p, i9 .f:ig 1.. Pect e(nChlamy jse)ffersoni uSsay.—Mansfie l1d9, 36:174-17 157, 8-179, author from carefully sampled sections of the Yorktown 184-185. Formation in Virginia, particularly along the James River, Chlam (yLsyropect ejenf)ferson i(uSsay).—Tucker-Rowla n1d9,38:19- 2p0i., and in North Carolina, where population samples collected 1 :figs .3-4 ,pi .5 :figs .19-20. in 1 foot (0.3 m) vertical intervals are available. Because of Chlam y(sLyropecte nje)fferson i(aSay).—Gardne 1r,944:32-3 4p 4,fii.: g2. the phylogenetic changes in this lineage and the lack of Chlamy jsefferson i(aSay).—Mongi n1,959:307-30 8p ,2i. 7fi: g3.. Chesapecte jneffersoni u(Ssay).—Wa radn Bdlackwelde 1r9, 75:13-1 p 51,i,. detailed stratigraphic sampling information for the Lee pi .2 :figs .1-3 ,pi .5 :figs .3-7 ,pi .7 :figs .3 ,10. Creek specimens, the three common taxa of the C. jefferson¬ ius species group are compared only in general subspecific Description.— Shell Outline: Shell large, attaining or specific terms. Detailed subspecific phylogenetic trends height of 152 mm; both valves of moderate convexity, with between populations will be discernible in the precisely left valve more convex than right; convexity reaching 37 collecte sdections. mm in left valves and 32 mm in right. Outline of disk almost Although both valves are convex, the left valve is more equilateral with slight posterior obliqueness; shells slightly convex than the right with a ratio of convexity of 0.77 to longer than high, more pronounced in larger specimens. 0.83 between the valves in mature specimens and an even Moderate disk gape anteriorly and posteriorly, reaching 5 greater left convexity in younger individuals with ratios as mm in larger specimens. low as 0.63. The strong developed plicae are broadly Auricles and Outer Ligament: Right anterior auricle with rounded in the stratigraphically earlier forms of this sub¬ planar surface; dorsal margin slightly dorsal to groove of species, but become more squared with flattened tops and outer ligament and slightly folded; byssal notch shallow with nearly vertical sides in the higher parts of zone 1 where C. broad, subangular apex; byssal fasciole poorly developed; jeffersonius septenarius develops from it. In the population ctenolium with 3 or 4 teeth well developed in specimens up sample of C .jeffersonius jeffersonius from the pit ,the number to 80 mm height, absent in larger individuals. Left anterior of plicae varies from 8 to 12 (Figure 23) with a mean of auricle with concave surface; dorsal margin flat and coinci¬ 10.1 for a sample of 139 valves. dent with trace of outer ligament; free margin slightly Some individuals in populations o fC .jeffersonius jefferson¬ curved with a broad, shallow byssal sinus. Posterior auricles ius from the upper part of Mansfield’s zone 1 exhibit similar in size to anterior, except posterior are slightly characteristics transitional to those found in C. jeffersonius higher; surfaces planar to slightly concave; free margins septenarius, which is the prevalent form in the lower part of nearly straight and perpendicular to hinge line. Anterior zone 2 of Mansfield. Samples of C. jeffersonius jeffersonius and posterior outer ligaments about equal in length. are characterized by a greater number of plicae, with a Exterior Shell Surface: Valves with 8 to 12 large plicae; mean of 10.1 versus 6.9 for C. jeffersonius septenarius in the in early stages of growth plicae have vertical sides and are Lee Creek samples, but there is some overlap between the sharply defined from interspaces; in later stages plicae be¬ two subspecies (Figure 23). Typical members of C. jefferson¬ come more rounded and sides have about a 45 degree slope; ius jeffersonius have plicae rounded in cross-section, lacking plicae slightly wider than interspaces. Radial costae strongly the flattened tops and square sides characteristic of C. developed on shell with a scabrous appearance where jeffersonius septenarius (Plate 22: figures 3, 4), although crossed by concentric lamellae; costae number as many as there is gradation between the two forms in the youngest 20 on the plicae, with up to 5 on the sides of the plicae, and members of C. jeffersonius jeffersonius. The plicae in C. as many as 18 in the interspaces; costae of varying strengths jeffersonius jeffersonius are actually broader than those of C. but generally uniform. Concentric lamellae well developed jeffersonius septenarius, probably due to the vertical sides in over the valves. Auricles have about 25 costae of about the latter form. In C. jeffersonius jeffersonius the plicae are equal strength with well-developed concentric lamellae giv¬ lower in relation to the width (Figure 24). The height of 70 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY INDIVIDU AOLFSNUMBER NUMB OPELRFICAE the plicae in relation to width becomes proportionally less the two groups are considered chronologic subspecies in the larger, older individuals. The scabrous nature of tbe rathe rthan separate species. costae is less developed in C. jeffersonius jeffersonius. The Stratigraphic and Geographic Range.— In the Lee convexity of the valve is slightly less in both the right and Greek Mine, specimens occur commonly in units 1 to 3 of left valves of ' C. jeffersonius jeffersonius, but this appears to the Yorktown Formation of Gibson (1967); specimens in be primarily a result of greater height of the plicae in C. unit 3 are transitional to C. jeffersonius septenarius. This jeffersonius septenarius rather than to a basically more con¬ subspecies has been reported from Mansfield’s zones 1 and vex shape of the valve. 2 of the Yorktown Formation in Virginia and North Caro¬ In other shell characters, such as length of hinge line, size lina. It is likely that most or all of the occurrences in zone of auricles, and shape of disk, no differences could be noted 2 should be referred to C. jeffersonius septenarius and that between the two subspecies .C .jeffersonius septenarius tends ('■ jeffersonius jeffersonius is characteristic of zone 1 only. In to have a deeper byssal notch with increasing size, but larger addition, the subspecies is found in roughly time-equivalent populations of both subspecies with an intact byssal notch Pliocene strata southward through South Carolina and will be necessary to confirm this. Georgia into Florida. Because of the general similarity of morphology between Measured Material.— Total specimens measured of the two subspecies, except for characteristics of the plicae, Chesapecten jeffersonius jeffersonius include 27 right valves and because even in the plicae there is transition between and 19 left valves (USNM 363017, 363019-363021) from the two groups in the upper part of zone 1 of Mansfield, IJSGS 25338 and 1 right valve and 1 left valve (USNM NUMB E6R1 71 C. j eff ersoni us jeffersonius • right valve O left valve C. jeffersonius septenarius ▲ right valve A left valve mm Figur e24 —. Bivariat escatte rdiagram showing th egreate rheigh to fth eplic ain relation to th ewidth in Chesapecte jneffersoniu sseptenariu tsha i nCje.ffersoniu jseffersoniu fsro mth Yeorktow Fnormatio inthe Le Ceree Mk ine. Tab l1e5.—Measurement (si nmm o )rafepresentativ seamp loef 363018) from USGS 25339. Both USGS collections are Chesap jecffterns joenffieurssonius. from spoil banks of Yorktown Formation in the Lee Creek Mine, North Carolina. Measurements (in mm) from a rep¬ resentative sample of 6 valves are given in Table 15. Character Chesapecten jeffersoniu sseptenariu s(Say) Plate 21: figures 7 ,8; Plate 22: figures 2, 3; Plate 23: figures 1-3, 6, 7; Plate 24: figures 1, 2; Plate 25: figure 5; Plate 26: figure 2 Pecte nseptenariu Ssay 1,824:136 p, i9 .f:ig 3.. Pect eJenfferson iuv asre.ptenar iSuasy.—D a1l8i,98:722. Pect (eCnhlam yjesf)ferson isuesptenar iSuasy.—Mansfie 1ld9,36:174-175, 179,184-185. Chlam (Lyysropect ejenf)ferson siuesptenar (iuSasy).—Tucker-Rowland, 1938:20-21 p, i3. f:ig 1. 5. Chesapecte sneptenari u(Ssay).—Wa radn Bdlackwelde 1r9, 75:15-1 p6,i. 6:figs .5-7 ,pi .7 :figs .2 ,9. Description. —Shell Outline: Shell large, attaining height of 132 mm; both valves convex, with left valve moderately convex and right valve of low convexity. Outline of disk almost equilateral with slight posterior obliqueness; 72 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY shells slightly longer than high, more pronounced in larger jeffersonius septenarius are higher in relation to the width specimens .No disk gape. (Figure 24), and have a squared cross-sectional profile with Auricles and Outer Ligament: Right anterior auricle with flattened summits and vertical sides. In the early and middle planar surface; dorsal margin nearly coincident with groove stages of ontogeny the plicae exhibit an overhang at the of outer ligament and slightly folded; byssal notch of mod¬ edge (Plate 22: figure 3), although the plicae become more erate depth with subangular apex; byssal fasciole poorly rounded in later growth stages. Other morphologic differ¬ developed; ctenolium with 3 or 4 teeth well developed in ences are the presence in C .jeffersonius septenarius of a more specimens up to 75 mm height, absent in larger individuals. strongly developed scabrous ornamentation ,a deeper byssal Left anterior auricle with concave surface; dorsal margin notch and sinus, and the thickening of the early part of the flat and coincident with trace of outer ligament; free margin interior of the shell by additional shell layers. The shell curved with a moderately broad and shallow byssal sinus. thickening is similar to that found in C. madisonius, but it Posterior auricles similar in size to anterior; surfaces planar does not reach the thickness found in later forms of C. to slightly concave; free margins curves. Anterior and pos¬ madisonius. terior outer ligaments about equal in length. Moderate An additional subspecies from the Yorktown Formation, auricular gape anteriorly and posteriorly. C. jeffersonius palmyrensis, was described by Mansfield Exterior Shell Surface: Valves with 6 to 8 large plicae; in (1936) from Palmyra Bluff on the Roanoke River in North early growth stages plicae have vertical sides and a flat Carolina, a locality he placed in the lower part of his zone summit with an overhanging edge; in later stages plicae lose 2. The holotype is the only known complete specimen in the overhanging edge and may retain vertical sides or the USNM collections. It was characterized by Mansfield as become slightly sloping; plicae slightly wider than inter¬ having four high, very broad plicae with flattened summits. spaces. Radial costae are strongly developed on shell and The plicae have overhanging edges in the umbonal area. have a scabrous appearance where crossed by the concentric Although Mansfield mentioned only four plicae, there is a lamellae; costae number as many as 20 on the summit of small plica on each margin of the holotype, which is re¬ the plicae, up to 9 on the sides of the plicae, and as many flected on the interior of the shell, giving a count of six as 1 5 in the interspaces; costae are of varying strengths and plicae by the writer’s method. Fragments of valves having additional ones come in by intercalation. Concentric lamel¬ similarly large plicae have been found at several localities lae well developed over the valves. Auricles have about 25 in the Yorktown Formation in North Carolina. Because of costae of about equal strength; well-developed concentric the absence of adequate samples, it is uncertain whether the lamellae give a scabrous appearance. Disk flanks steep and holotype is an extreme variant of C. jeffersonius septenarius covered with fine costae. Interior Features: Resilial insertion about 1 'A to 2 times as high as long; oriented with a slight posterior slope; single Tab l1e6.—Measurement (si nmm o )rafepresentativ seamp loef weakly developed auricular denticle both anteriorly and Chesap jecffterns soenpiutesnarius. posteriorly. Discussion.— A gradational change in the characteristics of C. jeffersonius occurs vertically through the Yorktown Character Formation. In the uppermost part of Mansfield’s zone 1, the population samples contain some individuals with fewer plicae that have square sides and are moderately high in the early ontogenetic stages. In the lower part of zone 2 these characteristics are well developed throughout the ontogeny of most individuals and dominate the populations. The populations in zone 2 are considered a chronologic subspe¬ cies, C. jeffersonius septenarius, in which the gradational change from its predecessor ,C .jeffersonius jeffersonius ,takes place during the upper part of zone 1. Chesapecten jefferson¬ ius septenarius is very similar to its ancestral form in most characteristics, but it is decidedly different in the characters of the plicae. The younger subspecies has fewer plicae, ranging from 6 to 8 with a mean of 6.9 (Figure 23) for the Lee Creek sample compared to a range of 8 to 12 with a mean of 10.1 for the sample of C. jeffersonius jeffersonius from the Lee Creek Mine. In addition, the plicae in C. NUMB E6R1 73 or subspecifically distinct. For the present it is retained as a in later growth stages plicae have rounded summits and separa tteaxon. sloping sides; plicae wider than interspaces. Radial costae Stratigraphic and Geographic Range —In the Lee well developed on shell and have a scabrous appearance Creek Mine, specimens occur fairly commonly in units 3 to where crossed by the concentric lamellae; costae number as 5 of the Yorktown Formation of Gibson (1967). Specimens many as 10 on the summit of the plicae, up to 4 on the sides of this subspecies are common in the lower part of Mans¬ of the plicae, and as many as 7 in the interareas; costae are field’s zone 2 of the Yorktown Formation but become rare of varying strengths and additional ones come in by inter¬ in the upper part of the zone. The subspecies is found in calation. Concentric lamellae well developed over the the Yorktown Formation from the York River in Virginia valves. Auricles have as many as 30 costae of about equal southward to the Lee Creek Mine in North Carolina. strength; well-developed concentric lamellae give a scabrous Measured Material —Total specimens measured of appearance. Disk flanks steep on left valves, moderately Chesapecten jeffersonius septenarius include 20 right valves sloping on right, covered with costae. and 15 left valves (USNM 218910, 218915, 363022- Interior Features: Resilial insertion about IV 2 times as 363024) from USGS 25338, collected from spoil banks of high as long; oriented with a slight posterior slope; single the Yorktown Formation in the Lee Creek Mine, North weakly developed auricular denticle, both anteriorly and Carolina. Measurements (in mm) from a representative posteriorly. sample of 6 valves are given in Table 16. Discussion. —Ward and Blackwelder (1975) reinstated the name C. madisonius Say on the basis of this name having Chesapecten madisoniu s(Say) been applied to a different species than what they deter¬mined to be the type lot in the Academy of Natural Sciences Plate 22: figure 1; Plate 24: figures 3-5; Plate 25: figures 1-4, 6; o Pf hiladelphia. Plate 26 :figures 1 ,3-5 As Mansfield (1936:184) indicated, C. madisonius (= C. edgecombensis of authors subsequent to Say) is part of the C. Pecte Mn adisoniu Ssa y1,824:13 [4no Ptecle mn adisoniu osafutho rssubse¬ que n tSotay]. jeffersonius lineage and appears at approximately the same Pec Etedngecombe nCsoisn r1a8d6,2:291. time as C. jeffersonius septenarius. The appearance of the Pec tjefnferson eiudsgecomben Csoisnrad.—Mansfi e1l9d3, 6:174-1 17759, , two taxa indicates a splitting of the C. jeffersonius stock 184-185. according to Mansfield’s (1936) phylogeny. Although pop¬ Chl a(Lmyyrospe cjetfefne)rs oendiguescomb e(Cnosnisrad).—Tucker-Rowland, ulations of C. jeffersonius septenarius are characterized by 1938:15-16 ,pi .2 :fig .5 ,pi .4 :fig .6. Chesapecte mnadisoni u(Ssay).—Wa radn Bdlackwelde 1r9, 75:16-1 p 86,i:. fewer plicae compared to the present C. jeffersonius jeffer¬ figs .1-4 ;pi .7 :figs .1 ,7 ,8. sonius stock, populations of C. madisonius have a greater number of plicae. C. madisonius from the Lee Creek Mine Description — Shell Outline: Shell of large size, attain¬ have from 10 to 17 plicae with a mean of 14.8 compared ing height of 133 mm; both valves of low to moderate to 10.1 for C. jeffersonius jeffersonius (Figure 23). Strati- convexity, with left valve more convex than right; convexity graphically younger populations of C .madisonius from other reaches 27 mm in left valves and 23 in right. Outline of localities have a higher mean number. The plicae in C. disk equilateral; shells slightly longer than high, more pro¬ madisonius are considerably lower than in subspecies of C. nounced in larger specimens. No disk gape. jeffersonius, and they are rounded in cross-section (Plate 22: Auricles and Outer Ligament: Right anterior auricle with figures 1-4) in contrast to the squared plicae in the time- planar surface; dorsal margin nearly coincident with groove equivalent populations o fC .jeffersonius. of outer ligament and slightly folded; byssal notch of mod¬ The anterior and posterior auricles of Chesapecten madi¬ erate depth with subangular apex; byssal fasciole poorly sonius are essentially equal in height on each value in con¬ developed; ctenolium with 3 or 4 teeth well developed in trast to the right valve of both subspecies of C. jeffersonius specimens up to height of 65 mm, absent in larger individ¬ in which the posterior auricle is higher than the anterior uals. Left anterior auricle with concave surface; dorsal one. The depth of the byssal notch is comparable to C. margin flat and coincident with trace of outer ligament; jeffersonius, but it is most similar to the population of C. free margin curved with a broad and moderately shallow jeffersonius septenarius ,which has a slightly deeper notch. C. byssal sinus. Posterior auricles similar in size to anterior; madisonius is also similar to C. jeffersonius septenarius in the surfaces planar to slightly concave; free margins straight thickening of the shell by the addition of calcite to the inside and perpendicular to hinge line. Anterior and posterior of the valve. In C. madisonius the thickness becomes greater outer ligaments about equal in length. Moderate auricular in the later forms and is considerably thicker than found in gape anteriorly and posteriorly. the other forms of the lineage. Although the convexity of Exterior Shell Surface: Valves with 10 to 17 plicae; in the valves is similar between C .madisonius and C .jeffersonius early growth plicae have vertical sides with a flat summit; jeffersonius, it is consistently less in the former than in the 74 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY time equivalent populations of C. jeffersonius septenarius. Chesapecten coccymelu s(Dali) The right valve of C. madisonius is comparatively less convex than the left in relation to C. jeffersonius. Plate 2s7-30 The scabrous ornamentation is not as strongly developed Pecten (Chlamys )coccymelu sDal i1, 898:741-742 p, i3. 4 f:ig 1. G. lenn, in this species as it is in C. jeffersonius. The early and middle 1904:374-375 p, i9. 9 f:ig 3. . ontogenetic stages of C. madisonius have only three costae Chlam y(sChlamy sc)occymelu (sDali).—Rowlan d19, 36 b1:007-100 p8 8,i.: on the summits of the plicae (Plate 24: figure 5), and are fig 3s-.4. probably the source of reports of C. madisonius (= C. nefrens Chlam (yLsyropecle mn)adisoni ubsassl eTruicker-Rowlan 1d9,38:13-1 p4i,. of Ward and Blackwelder) from the Yorktown Formation. 5 f:ig 1. .Chesapecte cnoccymel u(Ds ali).-—Wa radn Bdlackwelde 1r9, 75:8- p 9f3i,:g. s The increased number of costae on the plicae during on¬ 1,2 ,pi .7 :figs .14 ,15. togeny arise by intercalation. The lesser number of costae in C. madisonius mainly is a reflection of the greater number Description. — Shell Outline: Shell of medium size, at¬ of plicae, and thus narrower width of each plica. taining height of 58 mm; both valves of moderate convexity, In most characteristics the population of C. madisonius with left valve more convex than right. Outline of disk from the Lee Creek Mine is of an early to middle stage of equilateral; smaller valves slightly higher than long, larger development, not the latest, of the C. madisonius lineage. valves of equal height and length; slight disk gape anteriorly Stratigraphic and Geographic Range. —In the Lee an dposteriorly. Creek Mine, this species is found in units 3 to 5 of the Auricles and Outer Ligament: Right anterior auricle with Yorktown Formation of Gibson (1967), where it is moder¬ planar surface; dorsal margin slightly dorsal to groove of ately common. The species occurs in Mansfield’s zone 2 of outer ligament and strongly folded; byssal notch deep with the Yorktown Formation from the York River in Virginia an anuglar apex with a 60 to 90 degree angle; byssal fasciole southward to the Lee Creek Mine in North Carolina. It is broad, arched near disk, concave away; ctenolium with 4 or a useful guide fossil to zone 2. 5 teeth well developed throughout all growth stages. Left Measured Material. —Total specimens measured of anterior auricle with concave surface; dorsal margin flat Chesapecten madisonius include 7 right valves and 7 left and coincident with trace of outer ligament; free margin valves (USNM, 218908, 218916, 218919, 363025) from slightly curved with a shallow byssal sinus. Posterior auricles USGS 25338, collected from spoil banks of Yorktown For¬ much smaller than anterior; surfaces planar to slightly con¬ mation in the Lee Creek Mine, North Carolina. Measure¬ cave; free margins nearly straight, with posterior slope. ments from a representative sample of 6 valves are given in Anterior outer ligament about 1'A to 2 times as long as Table 17. posterior. Exterior Shell Surface: Valves with 17 to 19 prominent plicae; plicae have vertical to steeply sloping sides through¬ out the valve; plicae slightly wider than interspaces. Radial Tabl e17.—Measurement (si nmm o )arfepresentativ esampl eof costae strongly developed on shell, with coarsely scabrous Che smapaedcisteonius. appearance where crossed by the concentric lamellae ;costae vary in number from 1 to 4 on the summits of the plicae with 3 being the most common; early ontogenetic stages Character may have only 1 costa on each plica, with the 2 lateral ones being added later; the median costae on the plicae are stronger in development than the lateral ones; the sides of the plicae have 1 to 3 finely scabrous plicae; the interspaces commonly have 3 scabrous plicae with the central one being considerably stronger; all costae have strongly projecting spines, which may be recurved toward the umbo. Right anterior auricle has 6 coarse costae and may have 1 or 2 weakly developed ones intercalated between the more ven¬ tra lstrong ones; wel ldeveloped but weakly spitiose lamellae; other auricles with 8 to 15 fine costae, strongly spinose. Disk flanks on right valves have moderate slope, and have several fine costae; left valves have steep disk flanks with 5 or 6 scabrous costae. Interior Features: Resilial insertion somewhat higher than long; oriented with a slight to moderate posterior slope; single auricular denticle weakly developed both an¬ teriorly and posteriorly. NUMB E6R1 75 Discussion.— A number of workers, including Tucker- 1938, is one of the ornamental variations of Cheaspecten Rowland (1938), Schoonover (1941), and Mongin (1959) coccymelus found in bed 10 at Plum Point. The holotype of have separated the populations of Pecten madisonius (= C. C. m. bassleri (Plate 29: Figures 1-3) has a median row of coccymelus) that occur in the Calvert and Choptank forma¬ large spines surrounded by two lateral rows of smaller spines tions in Maryland into two groups, primarily on the basis of on the more ventral part of the valve, but the early part of shell size and ornamentation. These consist of a group of the valve up to a distance of approximately 17 mm from small, thin-valved specimens with rows of distally concave the origin of growth has the single row of spines character¬ spines found in the middle part of the Calvert Formation istic of C. coccymelus. This specimen also illustrates the (bed 10 at Plum Point), and a second group of considerably variation found in the rows of spines in the interspaces; larger ,thicker-valved specimens with considerably less scaly some interspaces have one dominant row of spines, while ornamentation, which occur in the upper part of the Calvert other interspaces have two or three essentially equally de¬ and the overlying Choptank Formation. Schoonover (1941) veloped rows o fspines. and Mongin (1959) did not propose new names for these The specimens found in the upper part of the Pungo groups, although they noted the differences between them. River Formation in the Lee Creek Mine include three Tucker-Rowland (1938:1 1) did use Chlamys (Lyropecten) complete right valves and fragments of other specimens. madisonius acanikos (Gardner), a form originally described These specimens from the Pungo River Formation compare from the Miocene deposits in Florida, for part of the group well with the population samples from bed 10 of the Calvert found in the Calvert Formation at Plum Point. She (Tucker- Formation at Plum Point, Maryland. A population study Rowland, 1938:13) also named a new subspecies, Chlamys was made involving 17 morphologic characters, and the Lee (Lyropecten) madisonius bassleri, for part of the complex Creek specimens fall well within the range of variation of group found in the Calvert Formation. Chlamys coccymelus the population sample from the Calvert Formation in all was considered to be a rare, but close relative of the other characters. The depth of the byssal notch is one of the more forms found in bed 10. important characteristics distinguishing C .coccymelus from Ward and Blackwelder (1975) proposed that the speci¬ the stratigraphically younger species of Chesapecten. Com¬ mens within the populations from bed 10 of the Calvert parison of the specimens from the Pungo River Formation Formation had a continuous range from forms carrying in North Carolina and the Calvert Formation in Maryland three rows of distally concave spines to the forms of Chesa- indicates no difference in this character (Figure 25). Other pecten coccymelus ,which is an end member carrying only one characteristics exhibit a similar pattern. The specimens row. This would include most of the bed 10 forms in the from the Pungo River Formation in North Carolina have a senior name, C. coccymelus. My examination of population consistency in the ornamentation ,with three well-developed samples taken from bed 10 at two localities near Plum Point rows of spines on the plicae of the right valve (with a fourth supports this treatment. The type specimen of C. coccymelus being found on the largest valves) and a dominant row of (Plate 29: Figure 5) is a relatively small left valve, 30 mm spines in the middle of the interspaces. The samples from high, which has only one row of spines on the plicae. It has the Pungo River Formation does not contain all of the a row of moderate spines in the interspaces and one or variation in ornamentation found in the samples from the more rows of smaller spines. The more common forms of Calvert, such as single rows of spines on the plicae, but this small Chesapecten found in bed 10 have three rows of spines could be due to the relatively small number of specimens on the plicae, although the three rows usually are not equal, recovered. the central row being larger than the two lateral ones. The Stratigraphic and Geographic Range. —This species two lateral rows of spines are added at some distance from is found in the upper 6 to 12 feet (1.8 to 3.7 m) of the the origin of growth and become progressively stronger in Pungo River Formation in the Lee Creek Mine. It is fairly development (Plate 30: Figures 2-4). The place of insertion common in the bryozoan shell hash zone that comprises the of the two lateral rows may be within a few millimeters of uppermost 2 to 3 feet (0.6 to 0.9 m) in the test pit (unit 7 the origin of growth or as much as 20 mm below the point. of Gibson, 1967), and also in the limey and indurated In smaller individuals single rows of spines on the plicae are intervals in the underlying interbedded limestone and phos- common. The development of a single row of spine is phatic sand units (units 4 to 6). This species previously has predominantly conFined to the left valves. The type speci¬ been reported from the middle and lower parts of the men of C. coccymelus is a left valve, which would contribute Calvert Formation, occurring in bed 10 (Ward and Black- to the extreme form of ornamentation. Most right valves welder, 1975:9) and possibly as far down in the Calvert as have three rows of spines but a few have four rows (Plate bed 2 (Schoonover ,1941:196 ,reported as Chlamys madison¬ 28: Figure 3). Another variation in the ornamentation is the ius). It is a reliable index to the Calvert Formation and common appearance on a single individual at a similar serves a similar function in the Pungo River Formation in growth stage of plicae bearing three rows of spines and North Carolina. plicae having just a single row (Plate 30: Figure 3). Measured Material —Total specimens measured of Chlamy s(Lyropecten )madisoniu sbassler Ti ucker-Rowland, Chesapecten coccymelus include 3 right valves (USNM 76 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY Figur e25 —. Bivariat escatte dr iagram showin gsimilarit yo df ept ho tfh ebyssa nl otc hbetwee nsample sof Chesapecte ncoccymelu fsrom th Cealve rFtormation M, aryland a,n dfrom th Peung oRive Frormatio ni nthe Le Ceree Mk ine. Tab l1e8.—Measurement (si nmm o )rafepresentativ seamp loef Maryland. Measurements from a representative sample of Che csoapcceycmteenlus. 7 valves are given in Table 18. Character Chesapecten nefrens Ward and Blackwelder Plate 31 :figure 7 Pecte nMadisoniu s—. Conra d1,840:4 8p ,2i. 4F:ig [1n. o Ptecte nmadisonius S a1y8,24], Pecte (nChlamy sm)adisoniu .—s Glen n19, 04:37 p7 1,i0. 0fi :g1.—Mansfield, 1936:174-1 17874,. Chlam y(Lsyropecte nm)adison .i—a Tucker-Rowlan d19, 38:9-1 p 1f1,i:g. s. 1-2.—Gardner ,1944:32 ,pi .4 :fig .5 ,pi .9 :fig .7. Chlam y(Lsyropecte nm)adisoni u.—s Schoonov e1r9, 41:192-20 p12 fi,1.ig: s. 1-3 ,pi .22 :fig .4 ,pi .23 :fig .3. Chlamy ms adisoni a—. Mongin 1,959:309-31 4p ,2i. 6f:ig sla. -b. Chesapacte nefren Ws ar dan dBlackwelde r1,975:9-10 p, i2 .T:ig s4.-6 p, i. 3 :figs .4-7 ,pi .4 :figs .1-2 ,pi .7 :figs .6 ,13. Description.— Shell Outline: Shell large, with height of 95 mm; right valve of moderate convexity. Outline of disk equilateral; valve longer than high. Auricles and Outer Ligament: Right anterior auricle with planar surface; dorsal margin slightly dorsal to groove of outer ligament and strongly folded; byssal notch deep with 218922, 218924, 363026) from USGS 25338, 13 right angular apex with an 80 degree angle; byssal fasciole broad, valves from USGS 25344, and 19 right valves (USNM arched near disk, planar away; ctenolium with 4 teeth well 218925, 363027-363029) from USGS 25345. Those from developed in adult form. Right posterior auricle with planar USGS 25338 are from spoil banks of the Pungo River surface; dorsal margin slightly dorsal to groove of outer Formation at the Lee Creek Mine, North Carolina; those ligament; free margin straight, sloping posteriorly. Anterior from USGS 25344 are from the Calvert Formation, 1.5 outer ligament about 1 1/2 times as long as posterior. miles south of Plum Point, Maryland; those from USGS Exterior Shell Surface: Valve with 19 plicae; plicae of 25345 are from the Calvert Formation at Camp Roosevelt, moderate height with steep sides; plicae wider than inter- NUMB E6R1 77 spaces. Radial costae strongly developed on shell and have Genus Amusium Roding, 1798 a coarsely scabrous appearance where crossed by the con¬ centric lamellae; 3 costae on the summits of the plicae, the Amusium sp. 2 lateral ones being weaker in the early stages and of equal strength in the later; interspaces have 3 costae, with the Plate 31 :figures 3 ,4 central one being considerably coarser than the lateral ones; Discussion. —The material from the upper part of the costae have moderately projecting spines or scabrous ap¬ Pungo River Formation in the Lee Creek Mine consists of pearance. Right anterior auricle has 7 moderately coarse three fragments, each several inches in length. The Lee costae with low scabrous ornamentation; right posterior auricle has 12 fine costae with scabrous nature. Disk flanks Creek fragments differ in several characteristics from Amu¬sium mortoni (Ravenel), the common species of Amusium of moderate slope and having several costae. occurring in the Pliocene and Pleistocene deposits from Interior Features: Resilial insertion somewhat higher Virginia to Mexico (Gardner, 1944:39). Although the spec¬ than long, oriented approximately perpendicular to the imens from the Pungo River Formation have approximately hinge line; single auricular denticle weakly developed both the same moderate convexity of the valve and slight con¬ anteriorly and posteriorly. centric corrugation on the exterior of the valve without Discussion. —The single specimen found in the Lee radial ornamentation, they are considerably thicker in shell Creek Mine is probably typical of the stratigraphically ear¬ cross-section and have widely separated paired lirae inter¬ lier members of C. nefrens. C. nefrens differs from C. coccy- nally (Plate 31: Figure 3). This is in contrast to the thin shell melus in being larger in size, having a greater length in and the closely spaced double lirae found in A. mortoni relation to height of the disk, in having a longer posterior (Plate 31: figure 1). The fragments do not allow comparison auricle in relation to the anterior, in having low scabrous of other morphologic features. As A. mortoni has consist¬ costae on the plicae rather than rows of highly recurved ently thin valves and equidistant spacing of interior lirae spines, and in having a lower and less pronounced plicae. over its wide geographic and stratigraphic range, it appears Stratigraphic and Geographic Range. —One speci¬ that the Lee Creek specimens belong to a different and men was collected from the uppermost bed of the Pungo probably new species. Glenn’s (1904:373) report of speci¬ River Formation in the Lee Creek Mine (unit 7 of Gibson, mens of A. mortoni from the St. Marys Formation in Mary¬ 1967). Schoonover (1941) and Ward and Blackwelder land is in error, apparently as a result of misreading the (1975) give the stratigraphic occurrence of this species as labels (USGS 2831 and 2835 were read as 2331 and 2325); from bed 14 of the Calvert Formation to bed 19 of the the specimens in question actually come from the upper Choptank Formation in Maryland. In the Calvert Cliffs part of the Yorktown Formation near Suffolk, Virginia, in section in Maryland, C. coccymelus occurs in bed 10 (Ward line with other reports of the age of the species. Thus, the and Blackwelder, 1975:9) and probably below bed 10 Lee Creek material is considerably older in age than the (Schoonover, 1941:196, reported as Chlamys madisonius). reported range of A .mortoni. However, both species are found within the upper bed in Amusium precursor (Dali, 1898) occurs in the Miocene the Lee Creek Mine, although only C. coccymelus has been Chipola Formation in Florida, a unit close in age to the found below the upper bed. Pungo River Formation (Gibson, 1967:643; Akers, 1972:9). Measured Material. —Measurements of a single speci¬ Thus, A. precursor is of a generally comparable age to the men of Chesapecten nefrens (USNM 218932) from USGS specimens found in the Lee Creek Mine, but differs in 25749, Pungo River Formation at the Lee Creek Mine, having uniformly closely spaced internal lirae and finely North Carolina, are given in Table 19. impressed radial lines on the exterior. As Dali (1898) did not select a holotype or illustrate any specimens of A. precursor, a lectotype is here selected and a lectoparatype illustrated (Plate 31: figures 5, 6). The lecto¬ type is an articulated specimen, USNM 647532, from USGS 2213 in the Chipola Formation, one mile (1.6 km) below Character Bailey’s Ferry, Chipola River, Florida. A number of prob¬ lems are encountered in the selection of the lectotype. Among localities mentioned by Dali (1898:755) in his de¬ scription of the species are Alum Bluff, from which no material could be found in the museum collections, and others along the Chipola River. Gardner (1926:50) and other writers have taken USGS 2212 (Chipola Formation at Ten Mile Creek) as the type locality, possibly because the 78 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY label in the museum collections says “type locality” com¬ 2212 Calhoun County, Florida: Ten Mile Creek, 1 mile pared with ‘‘cotype locality” for USGS 2213; however, this (1.6 km) west of Bailey’s Ferry on the Chipola entry of unknown origin has no standing. In the USNM River. Frank Burns, collector, 1889. Chipola catalogue for the lots from these localities, the number of Formation. specimens listed is fewer than are now in the type lots, 2213 Calhoun County, Florida: Chipola River, 1 mile indicating that specimens were added to the type lots, (1.6 km) below Bailey’s Ferry. Frank Burns, col¬ whether before or after Dali described this species is not lector, 1889. Chipola Formation. known. The only specimen that can be identified unequiv¬ 2447c Calvert County, Maryland: Blakes Cliffs, about 3 ocally with Dali’s original material is the largest specimen miles (4.8 km) north of Plum Point wharf. from USGS 2213, which agrees with measurements given Burns and Harris, collectors, May 1892. Calvert in the original description. Therefore this specimen is Formation. picked as the lectotype. All the material in the lots from 2452 James City County, Virginia: “Grove Wharf” on USGS 2212, 2213, and 2564 will be considered lectopara- James River, 9 miles (14.5 km) west of Yorktown types as there is no feasible way to determine if, or which, and 9 miles (14.5 km) south of Williamsburg. specimens may have been added to the type lots, and all the Frank Burns, collector, 1892. Yorktown For¬ material appears to be conspecific. A lectoparatype is illus¬ mation. trated (Plate 31: Figures 5, 6) to show the interior lirae, as 2564 Calhoun County, Florida: McClelland Farm, 1 mile the lectotype is an indurated double valve, the interior of (1.6 km) below Bailey’s Ferry, Chipola River. which cannot be observed. Frank Burns, collector, 1889. Chipola Forma¬ Most recovered fossi lspecimens of Amusium are fragmen¬ tion. tary and do not show many of the shell characteristics, such 3915 Middlesex County, Virginia: river front at Ur- as byssal notch and auricles. From the present observations banna, between mouth of creek and wharf of it appears that the internal lirae are distinct specific char¬ Weems Line of steamers on Rappahannock acters. The three species examined here illustrate differ¬ River. Frank Burns, collector, 1903. Lowermost ences in internal lirae (Plate 31: figures 1, 3, 6). The paired part of Yorktown Formation (= “Virginia St. lirae in specimens from the Lee Creek Mine are separated Marys” beds of Mansfield). by wide interspaces, varying from 9 to 10 mm between 3924 Essex County, Virginia: right bank of Rappahan¬ pairs and also have a wide distance of 7 to 8 mm between nock River at a very high bluff locally known as lirae of a pair. The lirae in A. precursor do not appear in “Jones Point,” 1 mile (1.6 km) north or up the pairs, but as closely spaced independent ones, varying in river from “Bay Port” wharf, about 13 miles (21 spacing from 1 to slightly over 2 mm within a single speci¬ km) north of Urbanna. Frank Burns, collector, men. The lirae in A. mortoni occur in pairs, with a very close 1903. Lowermost part of Yorktown Formation spacing of 0.2 to 0.5 mm between the lirae within a pair, (= “Virginia St. Marys” beds of Mansfield). and with a relatively wide spacing of 3.5 to 5.0 mm between 8179 Essex County, Virginia: right bank of Rappahan¬ the pairs in the illustrated specimen (Plate 31: figures 1, 2) nock River about 0.5 mile (0.8 km) downstream with a height of 73 mm. Thus it appears that the character¬ from Jones Pt. or 0.5 mile (0.8 km) northeast¬ istics of the internal lirae are of considerable help in defining ward from Butylo. W.J. Lee, collector, 1918. the species, particularly because of the fragmentary nature Most of this material was picked up from beach, o fmos tspecimens. not obtained in place in bank. Lowermost part Stratigraphic and Geographic Range. —The only of Yorktown Formation (= “Virginia St. Marys” known specimens of this possibly new Amusium sp. occur in beds o fMansfield). the limy interbedded layers (units 4-6 of Gibson, 1967) in 10278 Anne Arundel County, Maryland: Howard Post the upper part of the Pungo River Formation in the Lee Office. John Shepherd, collector, 1922. Calvert Creek Mine. Formation. 10962 Liberty County, Florida: cut in road leading to List of Localities Watsons Landing. W.C. Mansfield and E.C. Bracewell, collectors, 1925. Choctawhatchee USGS Localities Marl. 11999 Bertie County, North Carolina: right bank of Cho¬ 2025 Darlington County, South Carolina: Shell Branch, wan River, 0.75 mile (1.2 km) below Mt. Gould 1 mile (1.6 km) east of Darlington Court House. Landing, from bed exposed from beach to 10 Frank Burns, collector, 1886. Duplin Formation. feet (3 m) above river beach. W.C. Mansfield, 2106 Cumberland County, New Jersey: marl beds near collector, 1929. Yorktown Formation. Jericho. Frank Burns, collector, 1887. Kirkwood 23468 Middlesex County, Virginia: collected along beach Formation. of Rappahannock River from Urbanna to fish NUMB E6R1 79 cannery. T.G. Gibson, D. Wilson, and R. Brody, fordville. Muriel Hunter, collector, ca. 1970. collectors, 1963. Float material mixed with Hol¬ Torreya Formation. ocene material, but most is Miocene, which has 25746 Beaufort County, North Carolina: Lee Creek weathered from bluffs. Mine, near Aurora, from northwest wall of test 23565 Anne Arundel County, Maryland: Paul Basford pit, 2 foot (0.6 m) bed of blue sand, 1 1 feet (3.4 Farm, on north side of Maryland Highway 424, m) above base of Yorktown Formation, under¬ about 1.2 miles (1.9 km) SE of Davidsonville. D. lain by channeled surface. T. Gibson, collector, Wilson and H. Yokes, collectors, ca. 1958. Cal¬ January 1964. Yorktown Formation (unit 3 of ver tFormation. Gibson ,1967). 25338 Beaufort County, North Carolina: Lee Creek 25747 Northampton County, North Carolina: bluff on Mine, near Aurora. Spoil banks, west of access right bank of Meherrin River about 3 miles (4.8 road to central part of pit. T. Gibson, collector, km) above the Highway 258 Bridge; sample August 1972. Pungo River and Yorktown for¬ taken in interval of blue clayey sand, 1 to 5 feet mations. (0.3 to 1.5 m) above water level. T. Gibson and 25339 Beaufort County, North Carolina: Lee Creek D. Wilson, collectors. May 1963. Lowermost Mine, near Aurora. Float from spoil piles. D. part of Yorktown Formation. Wilson and others, collectors, 1969-1973. 25748 Beaufort County, North Carolina: shell fragments Pungo River and Yorktown formations. from limey layers, spoil piles, Lee Creek Mine, 25344 Calvert County, Maryland: 1.5 miles (2.4 km) south near Aurora. Jack McLellan, collector, April of Plum Point. Charles Buddenhagen, collector, 1974. Pungo River Formation. 1965. Calvert Formation, bed 10. 25749 Beaufort County, North Carolina: Lee Creek 25345 Calvert County, Maryland: 0.5 miles (0.8 km) be¬ Mine, near Aurora. Jack McLellan, collector, low Camp Roosevelt- Thor Hansen, collector, April 1974. Uppermost part of Pungo River 1969. Calvert Formation, bed 10. Formation. 25364 Beaufort County, North Carolina: Lee Creek 25757 Beaufort County, North Carolina: Lee Creek Mine, on the right bank of the Pamlico River, Mine, near Aurora, Lot 211. Jack McLellan, 5.5 miles (8.8 km) north of Aurora; section on collector, 1970s. Upper calcareous layers of northwest wall of main pit, in 5 foot (1.5 m) Pungo River Formation. thick bed of gray sand, 16 feet (4.9 m) below the 25758 Bertie County, North Carolina: bluff on west side top of the pit. L.W. Ward and others, collectors, of Chowan River, about 0.5 mile (0.8 km) below February 1972. Yorktown Formation, upper Mt. Could Landing, at W.H. Fowler place (old she blled. Steele place), 3-5 feet (0.19-1.5 m) above beach. 25743 Beaufort County, North Carolina: Lee Creek T. Gibson and D. Wilson, collectors, 1 963. York¬ Mine. Jack McLellan, collector, 1970s. Spoil tow nFormation. piles. Pungo River and Yorktown formations. 25744 Anne Arundel County, Maryland: Paul Basford Farm, on north side of Maryland Highway 424, USFC Station about 1.2 miles (1.9 km) SE of Davidsonville; in small stream gully NW of tobacco barn. T. Gib¬ 2244 Western North Atlantic Ocean, SE of Long Island, son and others, collectors, July, 1968. Calvert U.S.A., 40°05'1 5" N, 70°23'00" W, 67 fathoms Formation. (121 m), green mud and sand, bottom temperature, 25745 Wakulla County, Florida: Taff Pit, south of Craw- 52.9° Literature Cited Ake Wrs,.H. Bergend Mah.Hl,. 197 2P.lankton iFcoraminifer an Bdiostratigraph o ySfom Neeogene 1956 S. tratigraph yo fPart so fD eSoto and Harde eCounties F, lorida. Formation sN,orther Fnlorid an Adtlant iCcoast aPllai nT.ulane U .GS.eologic Saul rv eByullet i1n0,30-B:65-98. Studie isGneolog ayn Pdaleontolog y9,(1-4 1):-13 9p,late 1s-60. Berggren W, .A a.,ndJ.A V.a nCouvering Banks J,.E .a, n dM.E H. unter 197 T4 h.Lea Nteeogen Pea. laeogeograph Pya, laeoclimatolog Pya, laeo- 197 3P.ost-Tamp aP,re-Chipo lSaedimen tEsxpose di nLibert yG, ads¬ ecolo g1y6,(1/ 12-)2: 16. de nL,eo na,n dWakul lCaountie sF,lorid aG.u Clfoa sAtssociation Blo Ww,.H. oGfeologic Saol cieti eTsransaction 2s3, :355-36 f3i,gur e1s-4. 1969 L.at eMiddl eEocen et oRecen Ptlankton iFcoraminifera Bl iostra- 80 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY tigrapl iPyr.oceedin goth sfFeir Isntternation Caol nferen co Penlank¬ 1944 M. ollusc afrom th eMiocen ean dLowe rPliocen eo Vf irgini aand ton iMc icrofossil sG,enev a1,96 7p,age 1s99-42 2p,late 1s-54. Nor tCharolin aP,a r1Pt:elecypod aU.. SG.eologic aSlurve Pyrofes¬ Cla rWk,.B. siona Plape r1,99-A 1;7 8page s2, 3plates. 190 4In. troductio ann Gdener aSltratigraph Ricelation Ms.arylan Gdeo¬ 1948 M. ollusc afrom th eMiocen ean dLowe rPliocen eo Vf irgini aand logic Saul rve My,iocen pea, g exsxiii-xxxii. Nort hCarolin aP,a r2 tS:caphopod an dGastropod aU. . SG. eo¬ Clark W, .B .a, nd B.L M. iller logic Saul rv ePyrofession Paal pe 1r9, 9-B:179—31 p0l,at e2s4-38. 1912 T. h ePhysiograph yan dGeolog yo tfh eCoasta Pl lai nProvinc eof Gibs oTn.G, . Virgin iVai.rgin Giaeologic Saul rv eByullet i4n:,13-222. 1962 B. enthon iFcoraminifer an dPaleoecolog yo tfh eMiocen eDe¬ Clark W, .B .B, .L M. iller L, .W S. tephenson B, .L J.ohnson a, nd H.N P. arker posit so tfh eMiddl eAtlanti cCoasta Pl lain 1.9 8pages D. octoral 1912 T. h eCoasta Pl lai no Nf ort hCarolina N. ort hCarolin aGeological dissertat iPornin, ce Utonniversity. an Edconom Sicurve 3y:,5 5p2ages. 196 7S.tratigraph ayn Pdaleoenvironmen o tfh Pehosphat iMc iocene Conra Td.A, . Strat oa Nf ort hCarolin aG. eologic aSlociet oy Afmeric Baulletin, 1833 .On Some New Fossi land Recen tShells o fthe United States. 78:631-650. America Jnourn a oSlfcienc aen Adrt s2,3(2):339-346. 1970 L.at eMesozoic-Cenzo iTcecton iAcspect os tfh eAtlant iCcoastal 1834 D. escription so Nf ew Tertiar yFossil sfrom th eSouther nStates. Marg iGne. ologic Saol cie Aotymf eri cBaullet i8n1,:1813—1822. Journa ol fth eAcadem yo fNatura Sl cience so fPhiladelphia, 197 1M. iocen oe tfh Me idd lAetlant iCcoast aPllain M. arylan dGeological 7 (113)0: -157. Sur vGeuyidebo 3o:k1,-15. 1840 F.ossi los tfh eMedia Tlertiar yo tfh eUnite dState s[,2]:33—56 p, lates 1983 aS.tratigraph o yMf iocen tehroug Lhowe Prleistocen Setrat oa tfhe 18-2 9P.hiladelphi aJu: da Dhobso n[T. h ceomple tweor k1,838— Unite dState sCentra Al tlanti cCoasta Pl lain I. nClayto nE R. ay, 1861 r,epublished w, it ha nintroductio nb yW H. D. al ia, sSpecial edito rG, eolog yan dPaleontolog yo tfh eLe eCree kMine N, orth Publicatio o ntfh We agne Frre Ienstitu to eSfcienc (ePhiladelphia, Caroli n S1am., ithsoni aCnontributio nPtosaleobiolog 5y3, :35-80, 1893 )x, vi i+i 13 6pages 4, 9plates.] f3ig7ures. 1842 O. bservation son aPortion o fth eAtlanti cTertiar yRegion w, ith 1983b K.e Fyoraminifer afrom Uppe Or ligocen et oLowe Prleistocene aDescriptio no Nf ew Specie so Of rgani cRemains B. ulleti no tfhe Strata o fthe Centra Al tlanti cCoasta Pl lain I.n Clayton E R. ay, Proceeding otshf Neation aInl stitutio fn otrh Peromotio onSfcience, edito rG, eolog yan dPaleontolog yo tfh eLe eCree kMine N, orth Washingto nD,.C 2.,:171-19 p42l,ates. Caro liSn Ima. ,ithsoni aCnontributio Ptnoasleobiolo g5y3,:355-454, 1845 F.ossi los tfh e[Media Tlertiar oyrJMiocen eFormatio no tfh eUnited 2 p2late Fs2,igures. State s[3, ]:57-8 0p,late 3s0-3 23,4-4 4P.hiladelphi aJu: da hDob¬ Glen Ln.C, . son [.Th ecomplet ework 1, 838-1861 r,epublished w, ith an 910 4P.elecypod aM.arylan Gdeologic aSlurve My, iocen ep,ag e2s74-401, introductio nb yW H. D. al ia, sSpecia Pl ublicatio no tfh eWagner pla 6te5s-108. Fre eInstitut eo Sfcience P, hiladelphia 1,893 x.vi i+1i 3 6pages 4,9 Gme lJi.nF,. plates.] 1791 G. aro lLiinnae Siystem aNatura epe Rregn aTri aNaturae E.dition 1862 D. escription so Nf ew Genera S,ubgener a n dSpecie so Tfertiary 1 v3o, lum 1e (V6e, rmes):3021-3910. an Rdecen Sthell sP.roceeding o stfh Aecadem o yNfatur aSlciences Grant ,U.S. ,IV ,and H R .Gale Pohfiladelph 1i4a(,6):284-291. 1931 C. atalogu eo tfh eMarin ePliocen ean dPleistocen eMollusc aof 1867 N. ote os nFoss iSlhel lasn dDescription os Nf ew Specie sA. merican Californ ian Addjacen Rtegion sM. emoi ro stfh Sea Dnieg Soociety Journ ao Clfoncholog y3,(2 81):8-190. o Nf atura Hl istory 1 ,1:03 6pages 3, 2plates. Da Wli,.H. Haz eJ.lE,. 1898 .Contribution sto the Tertiary Fauna o fFlorida with Especial 197 1P.aleoclimatolog oy tfh Yeorktow nFormatio n(Uppe Mr iocene Referenc eto th eSile xBed so fTamp aand th ePliocen eBed sof an dLowe Pr liocene o) Vf irgini an dNort hCarolina B. ulleti ndu th Cealoosahatche Reive Wr. agn eFrre Ienstitu t oSefcienc Terans¬ Cent rd eReecherch ed sPea (uFrance S)o, cie tNeationa dle ePsetroles action 3s(,4):571-94 p5l,at e2s3-35. d'A q5u(situapinpele,ment):361-375. 1904 .The Relations o fthe Miocene o fMaryland to Tha to fOther 1983 A. g eand Correlation o fth eYorktown (Pliocene )and Croatan Region asn dt oth eRecen Ftauna M. arylan dGeologica Slurvey, (Pliocen ean dPleistocene F)ormation as tth eLe eCree kMine I.n Mioce npea,g cexsxxix-clv. Clayton E R. ay e, ditor G. eolog yand Paleontolog yo fthe Lee DuB aJ.rR, . Chee Mk in eN,ort Charolin aSI.,mithsonia Cnontribution t sPoa¬ 1958 S.tratigraph yan dPaleontolog yo tfh eLat eNeogen eStrat ao tfhe leobiolog y5,3:81-20 03 p,8late Fs4i,gures. Caloosahatche Reiv eArre oaSfouther Fnlorid aF.lorid Gaeolog¬ Heilpr Ain., ic aSlurve Byulletin 4,0:26 p7age s1 ,p2lates. 1881 A .Revision o tfh eCis-Mississipp Ti ertiar yPecten so tfh eUnited DuBar J,.R .a, n dJ.R S. olliday State Psr.oceedin got hsfAecadem oNyfatur Sacl ienc ePshiladelphia, 1963 S. tratigraph yo tfh eNeogen eDeposits L,owe rNeus eEstuary, 33:416-422. Nor Ctharolin Sao. utheaste rGneolog 4y(,4): 231-233. 1887 E. xploration so nth eWes Ct oas ot Fflorid a n di nth eOkeechobee Emmo En.s, Wildernes Ws. agn eFrre Ienstitu t oSefcien cTeransaction 1s,:134 1858 A.gricultur eo tfh eEaster nCountie sT,ogethe wr it hDescriptions page s2, 3plate (s 2unnumbered i n,text). o fthe Fossil so fthe Mar lBeds .In North Garolina Geological 1888 T. h eMiocen eMollusc ao tfh eStat eo Nf ew Jersey P. roceeding sof Surve Ryepo r(tRaleigh 3),1 p4age s2,5 f6igures. th Aecadem oNyfatur Sacl ienc e oPsfhiladelph i3a9, (3):397-405. Flemi nCg.A, . Huddles tPu.Fn., 1957 T.h eGenu Psecte ni nNew Zealand N. ew Zealan dGeologica Slurvey 1976 T. h eNeogen eStratigraph yo fth eCentra Fl lorid aPanhandle Paleontologic aBlulleti n2, 6 :p9age s1 p,5lates. (Abstrac tT) h.Geeologic Saol cie Aotyfmeric Na,ortheaste rSnection Gardne ArJ.,. a nSdoutheaste Srnecti oAnnnu Maleetin Agb, strac wts iPthrograms, 1926 .The Molluscan Fauna o fthe Alum Bluf fGroup o fFlorida ,Part 8(2):203. 1 U. .S G. eologica Slurve Pyrofessiona Plape r1,42-A 7: 9page s1,5 Mansfie lWd,end eCl.l plates. 1929 aT.h Cehesapeak Me iocen Beasi no Sfedimentatio na Esxpressed NUMB E6R1 81 in th eNew Geologi cMap o Vf irginia W. ashington Academ yof em oy Nf atur aSlcience o sPfhiladelphi a9,4:167-25 0p,late 7s-22, Scien Jcoeurn 1a9l,:263-268. 9figure s1t,able. 1929b N. ew Foss iMl ollusk sfrom the Miocene o fVirginia and North Rodi nPg.F, . Carolina w, it h aBrie Of utlin eo tfh eDivision so tfh eChesapeake 179 8M. useu mBoltenianu msiv Ceatalogu csimelioru mteribu rsegn insa¬ Grou pP.roceeding o stfh Uenite Sdtate Ns ation aMl useum 7,4 1(4 -)1: tura qeua oeli mcolleger aJot aF.rie dB.olte nM, .D.p.d P.,a rSsecunda, 1 1p,l5ates. Conchyli av. i+ii11 p9age sH. amburg T:ypisJoha nChris tTirapii. 1932 M. iocen ePelecypod os tfh eChoctawhatche eFormatio no Fflor¬ Rowland H, . IS.e eTucker-Rowland H, .I. ida F.lorid aGeologica Slurve yBulletin 8 ,2:4 0page s3, 4plates. Sa yT,. 193 6S.tratigraph iScignificanc o eMf iocen eP,liocen ea,n Pdleistocene 1824 A. n Accoun to fSom eo fth eFoss iSl hell so fMaryland A. cadem yof Pectinida ienth Seoutheaster nUnite Sdtate sJo. urn ao Plfaleon¬ Natur aSlcience o sPfhiladelph iJaourna 4l,:124-15 5p,late 7s-13. to l1o0g:y1,68-192. Schoono Lv.eMr,. 1937 A. New Subspecie so fPecten from the Uppe rMiocene o fNorth 1941 .A Stratigraphi cStud yo fthe Mollusk so fthe Calver tand Chop- Carolin aW.ashingto Ancadem oSyfcienc eJosurna 2l7, :10-1 f2i,g¬ tan Fkormation os Sfouther nMaryland B.ulletin os Afmerican ur e1-s3. Paleontolog 2y5, (94B 1)6: 5-29 p8l,at e1s9-30. 1944 .Stratigraph yo fthe Miocene o fVirginia and the Miocene and Shattu Gc.kB,. Pliocene o fNorth Carolina I.n J G. ardner M, ollusca from the 1904 G. eologica aln dPaleontologica Rl elations w, it h aReview o Efar¬ Miocen ean dLowe rPliocen eo Vf irgini aan dNort hCarolina, li eInrvestigation Ms.arylan Gdeologic Saul rve My,iocen pea, ges Pa r 1tP:elecypod aU. . SG.eologic aSlurve Pyrofession aPlaper, xxxiii—cxxxvii. 199-A:1-19 f,igure s1-4 t,able s1-2. Tucke rH, . IS.e eTucker-Rowland H, .I. Mong Din. , Tucker-Rowl aHn.Id., 195 9S.tud oy Sfom Aemerica nMiocen Leamellibranch asn dCompar¬ 193 4S.om Aetlant iCcoa sTtertiar Pyectiniad eA.merica nMidlan dNat¬ iso wni tRhelate Eduropea Snpecie Bs.ulletin oAsfmerica Pnaleon¬ uralis t1,5:612-621 [.A sH. IT.ucker.] tolog 3y9, (180):283-34 p3l,at e2s4-27. 1936a T. he Atlanti cand Gul fCoas tTertiar yPectiniade o fthe United Moo Ere.J,. State As.merica Mn idlan Ndaturalis 1t,7(2):471-49 0p,late 1s-4. 1962 C. onrad’ Cs enozo iFcoss iMl arin eMollus kTyp eSpecimen as tthe [A Hs . IT.ucker.] Academ o yNfatur aSlcience o sPfhiladelphi aP.roceeding o stfhe 1936b T. h eAtlanti cand Gul fCoas tTertiar yPectinida eo fth eUnited Academ oNyfatur Sacl ienc e oPsfhiladelph i1a1, 4:23-120. State -s IAI.merica Mn idlan Ndaturalis 1t,7(6):985-101 7p,lates Olss oAn.A, . 5-10 [.A sH. IR. owland.] 1914 N. ew an dInterestin gNeocen eFossil sfrom th eAtlanti cCoastal 1938 .The Atlanti cand Gul fCoas tTertiary Pectinidae o fthe United Pla iBnu. lleti nAosmf eric aPnaleontolog 5y(,24):45-62. State Ms.emoir ed sMuuse Reoy aDl’Histoi rNeaturel ld eBeelgique, 1917 T. h eMurfreesbor oStag eo of u rEas Ct oas Mt iocene B. ulletin sof 10t hserie s1,3:1-76 p,late 1s-6. Amer Picaalenonto l5o(g2y8,):153-164. Tuomey M, .a, nd F S. H. olmes Olsson A, .A .a,n dA H. arbison 1855 P. leiocen eFossi lso Sfout hCarolin .a .P..ar 1t,3 0pages C. harleston, 1953 P. liocen eMollusc ao Sfouther nFlorid awit hSpecia Rl eferenc eto Sou tCharolin aR:usse alln Jdones. Thos fero mNort Shain Ptetersbur gA.cadem oyNfatur aSlciences Wall eTr.,R. o Pfhiladelph iMa onograp h 84,:5 p7age s6 ,p5lates. 196 9T.h Eevolutio no tfh Aergopecte ngibbu Sstoc (kMollusc aB:ivalvia), Pur iH, .S .a, n dR.O V. ernon wit hEmphas ios nth Teertiar ayn dQuaternar Sypecie os Efastern 1964 .Summary o fthe Geology o fFlorida and a Guidebook to the Nort hAmerica J.ourna o lPfaleontolog yM, emoi r3 ,1:2 5page s8, Class Eicxposure Fsl.orid Gaeologic Saul rv eSypec iPalublicatio n5, plates. (revised 3):1 p2age s1 p,1lates. Ward L,.W a.,n dB.W B. lackwelder Richa rHd.sG, . 197 5C.hesapeclen Na,e wGenu o sPfectinida (eMollusc aB:ivalvia f)rom 1950 G. eolog yo tfh eCoasta Pl lai no Nf ort hCarolina A. merica nPhilo¬ th eMiocen ean dPliocen eo Efaster nNort hAmerica U. .S G. eo¬ sophic aSlocie tTyransaction ns,e wserie 4s ,08 p:3ages. logic aSlurve Pyrofession aPlape r8,6 12 :p4age sp7,late sf2i,gures, 1968 C. atalogu eo Ifnvertebrat eFoss iTl ype sa th eAcadem yo Nf at¬ ta2bles. ura Slcience so Pf hiladelphia A. cadem yo Nf atura Slcience sof Whitfie Rld.P, . Philadelph Siapec iPalublicatio n82:2 ,p2ages. 1894 .Mollusca and Crustacea o fthe Miocene Formation so fNew Richard sH, .G a.,n dA H. arbison Jerse yU.. SG.eologic aSlurve yM, onograph s2,4:13-19 3p,late 1s- 194 2M. iocen Ienvertebrat Feaun oa Nf e wJerse yP.roceeding os Afcad¬ 24. PLAT EI Pecte mn clellan ni,e wspecie Ps,ung Roiv eFrormation, Le eCree kMine U, SG S25743 1 .Paratype U, SNM 218828 e, xterna vl iew o frigh tvalve X, 1.5. 2 .Paratype ,USNM 218829 ,externa lview o frigh tvalve ,X 1. 3 .Holotype ,USNM 218830 ,externa lview o frigh tvalve ,X 1. rf M I'ecte nhumphreys uwoo ml a l nlieilprin K,irkwoo dFormation |.erieho N, e wJerse Uy SNM 21883° U SCS 21 (Hi ,externa lv iew o lpartia lrigh tvalve ,x I Pate hnumphreys huumphreys Cuonra dC,alve rFtormatio nD,avidsonvill eM, arylan dU2:SNM 218833 , IS (.3 23565 ,externa lview o frigh tvalve .X I ,| ,USNM 21H835 ,lISCS 25744 external view ol partial right valve. X I ; 7. USNM 218838, USCS 23565. external view ol riirln /V t,e nhumphreys uhumphreys uCon aid P,ung oRive Ftormatio n ,Ie, e(aee kMine 3 :U, SNIV USCS 2533d ,externa lview o lpartia lrigh tvalve ,X I ,5 ,USNM 218836 ,USCS 25743 view o liigh lvalve ,X 2 ;6 ,USNM 218837 ,USCS 2533d ,externa lview o lpartia lrigh tv ■ 37 P,.ecte nhumphreys nhumphreys Ciionrad P,ung oRive Frormation I,e eCree Mk ine e,xterna vlie wof partia lleft valve: I ,USNM 218839 ,USGS 25339 ,X I; 2 ,USNM 218840 ,USGS 25339 ,x I; 3, USNM 218841 .USGS 25339 ,x I ;7 ,USNM 218845 ,USGS 25339 ,x I. 4- 6P.ecte hnumphreys hnumphreys Cnonra dT,orrev Faormatio nG,ravvfordvill eF,lorid aU,SG 2S5745: 4 ,USNM 218842 ,externa lview o fpartia lrigh tvalve ,X I ;5 ,USNM 218843 ,externa lview of partia lrigh tvalve ,X 1.5 ;6 ,USNM 218844 ,externa lview o fpartia lef tvalve ,X 1 .(From Banks an Hdunte 1r,973.) 8P.ecte hnumphreys hnumphreys Cnonra dC,alve rFtormatio nD,avidsonvill eM, arylan dU,SNM 218838 ,USGS 23565 ,interna lview o frigh tvalve ,X 1. 86 SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY PLAT E5 1, 2 4P,.ecte nhumphreys humphreys Ciionra dC,alve rFtormatio nD,avidsonvill eM, arylan dle, fvtalv e1:, USNM 218846 ,USGS 25744 ,externa lview ,X 1.5 ;2 ,USNM 218846 ,USGS 25744 ,internal view ,X 1.5 ;4 ,USNM 218838 ,USGS 23565 ,externa lview ,X 1. 3P.ecte nhumphreys wii oolman Hi eilprin K,irkwoo dFormation Je, rich oN, e wJerse yU, SNM 218847, USGS 2106 ,externa lview o flef tvalve ,X 2 (see also ,Whitfield ,1894 ,pi .4 :fig .7). Pecte nhumphreys iwi oolmam Heilprin K. irkwoo dFormation J,ericho N, ew Jerse ySI,C. S2106 1:, lSN M 218848 ,externa l \iew o lrigh t\al\e ,X 1 ;2 .3 ,L'SNM 218840 ,externa land interna lv iews o flef tvalve .X 1 (see also Whitfield .1804 .pi .4 :figs .8.0) :4 .L’SNM 218850 ,externa lview ol partia lrigh tvalve ,X 1 ;6 ,USNM 218848 ,resilia linsertion o frigh tvalve ,X 3. Pecte hnumphreys hiiumphreys Ciionra dP,ung Roive Frormatio nL,e Ceree Mk in eL,'SN M218851, USGS 25339 e, xterna vl iew o fpartia rl igh tvalve X, 1. Pecte hnumphrey shiiumphrey sCiionra dC,alve rFtormatio nD,avidsonsill eM, arylan dL,'SNM 218838 ,USGS 23565 ,interna lview o flef tvalve ,X I SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY Argopect eb eno r u.e isAell.bore uwsatsonens (iMs ansfield), Yorktow fnormatio nL,e Ceree Mk ine I lSNM 218852 ,USGS 25746 ,externa lview o lright valve ,X I, 2 . ISNM 218853 ,USGS 25338 ,externa lview o frigh tvalve ,X 1. lSNM 218854 ,USGS 25746 ,righ tvalve :3 ,resilia linsertion ,X 3 ;4 ,externa lview view x,I li . ISNM 218855 ,USGS 25746 ,righ tvalve ,resilia linsertion ,X 3. SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY 1 4A,.rgopecte enboreu dsarlingtonens i(sDal iD),upl iFnormatio nD,arlingto nS,out Charolin aU,SG 2S025: JI,cctotype U, SNM 145432 e, xterna vl iew o fanterio rportion o frigh tvalve X, 2 ;4 l,ectoparatype, USNM 218859 ,externa lview o flef tvalve ,X 1. 2 3 ,A.rgopecte neboreu afs fA .e.boreu solarioide (sHeilprin )Y,orlaow nFormation L,e eCree kMine U, SNM 218860 ,USGS 25339 :2 ,externa lview 'o frigh tvalve ,X 1 ;3 ,externa lview o flef tvalve ,X 1. 5A.rgopecte enboreu ysorkens i(sConrad Y),orktow Fnormatio nY,orktow nV,irgini ale, ctotyp eA,NSP 38007 ,externa lview o flef tvalve ,X ]. ,< 1rgopecte nfboftu asf f ,pF. boveu solovioidf (sHeilprin )5o,rktovs nFormation F,e eCree Mk ine SL.\\ 218860 .L SGS 25339 ,righ tvalve :1 .resilia linsertion ,X 3 ;2 ,interna lview ,X 1:3 .externa lview o anterio rventra pl ar t X,I. Aygopccte nebovru asf f ,fF.boreu ws atsonens i(sMansfield )\,orktow nformation F,e e(aee Mk int l.SNM 218861 F. ISC S25338 d, orsa vl iew o farticulated specimen x,1. Argnprttr nrhnrru stirhannaens n(Mansfield )“, \irgiii uS Mi arys b' ed s ill,i.imu V, irginia C, S C>S 391I ,le tini\ |ic , IS\ M 370829 ,externa lview o lrij^lu valve ,X 1.3 ,lettotvpe ,USNM 370829, irsili.i linsertion ,X 3 ;1 ,lettoparatype ,USNM 218802 ,resili.i linsertion o lel ivalve ,X 3. Argupetln rtlmreu as lA le.bareu ws larmtth (sHcilprin )Y,orktow nFormation L,e eCree kMine 2:, lSVM 2 IMXliO ,lS (,S 233311 ,dorsa lview o tarticulated specimen .X 1 ;5 ,lSNM 203904 ,lSC IS 2.330 I ,cMcriia lview o lritdi tvalve ,X I. SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY I'Uiatpecle n 1 1i nI nm u sdmtnniu s(Say () =/ d' m tur nu sdonah ltI(i itke R-i owland) )Y, o ki tow nFormation (.rove Wlta iI .Virginia ,liolotype o l/ ’r .donahli ,lSNM 114999 ,L SGS 2452 :1 ,externa lornamen I,moi lon ante )101 ventra lpar to fvalve .X 3 ;3 ,externa lview o lef tvalve ,X I. /Vr/r nmcleUam n, ew xpe ites I,’ung oRive rFormation L,e eCree kMine p, aralype U, SNM 218X95 ISGS 25743 ,exiema lview o llef tvalve .X I 5-7 P. lacopecte nclintoniu scltntoniu s(Say )Y.orktow nFormation L,e eCree kMine L,'SG S25338 1:, L'SNM 218886 i,nterna vl iew o flef tvalve X, 1 ;2 L, 1SNM 218866 r,esilia ilnsertion o flef tvalve, X 3 ;5 ,L SNM 218867 ,resilia linsertion o frigh tvalve ,X 3 ;6 ,USNM 218868 .resilia linsertion o flef tvalve ,X 3 ;7 ,USNM 218869 ,resilia linsertion o frigh tvalve ,X 3. 4 8. P. lacopecte nmagellamcu s(Gmelin )R, ecen ts,out ho Lfon gIsland 6, 7fathoms U, SF C2244 l,eft valve :3 U, SNM 703766-25L .resilia linsertion .X 3 ;4 L, 'SNM 703766-9L r, esilia linsertion X, 3 ;8 U, SNM 703766—16L i,nterna vl iew X, 1. NUMB 6E1R 1 P. lacopecte nsp a.f fP .m. agellamcu (sGmelin )Y,orktow nFormation L,e eCree kMine U, SNM 218873, USGS 25743 ,externa lview o frigli tvalve ,x 1, 2 P. lacopecte nmagellamcu s(Gmelin )R, ecen ts,out ho Lfon gIsland 6, 7fathoms U, SNM 703766- 1HR, USFC 2244 ,externa lview o frigh tvalve ,X 1. 5 .Chlamy sdecemnaria (Conrad) Y, orktown Formation L, ee Creek Mine U, SGS 25338 :3 .USNM 218874 ,rest Iia Iinsertion o fright valve ,X 2 ;4 ,USNM 218875 ,externa lview o fright valve of articulated specimen ,X 1 ;5 ,LJSNM 218875 ,externa lview o flef tvalve o farticulated spec¬ imen X. 1 . ]P. lacopecte nmagellanicu (sGmelin )R, ecen ts,out ho Lfon gIsland 6, 7fathom sU, SNM 703766-16R USFG 2244 ,interna lview o frigh tvalve ,X 1. 2P.ecte nhumphreys wii oolman Hi eilprin K,irkwoo dFormation Je, rich oN, ew'Jerse yU,SNM 218847 USGS 2106 ,interna lview o flef tvalve ,X 2 (see also WhitField ,1894 ,pi .4 :fig .7). 3 P. lacopecte nsp a.f fP .m. agellanicu (sGmelin )Y,orktow nFormation L,e eCree kMine U, SNM 218873 USGS 25743 ,interna lview o frigh tvalve ,X 1. 5 A. rgopecte neboreu asf fA .e.boreu solarioide (sHeilprin )Y,orktow nFormatio n(uppe srhe lbled) Lee Creek Mine U, SNM 218876 U, SGS 25364 :4 e, xterna vl iew o flef tvalve X, 1 ;5 r, esilia ilnsertion Wiilifa'li SMITHSONIA NCONTRIBUTION TS OPAI.EOBIOI.OGY (ihlam dyesremna r(mConra Ydo),rkio wLonrmation Le eCree kMine U. SG S25338 I-Menial view nl i valve, X 1: I. I SMI 218871; 2, 1 SNM 218882; 3, USNM 218883; 1 I SNM 218881; a .I SNM 218885; 0 USNM 2 I8880 ;7 .USNM 21HKH7 ;8 ,L ISNM 218888 ;II ISNM 218889 ;10 .L SNM 218874 ;II lSNM 218890 ;12 ,USNM 218891 ;13 ,USNM 218892. 1C..hlamy dsecemnar i(aConrad ( )I=’ecte nvirgimanu (sConrad )Y,orktow nFormation C,i tP\oin tV.ir¬ ginia h, olotype A, NSP 1620 e, xterna vl iew o frigh tvalve x ,I -9 (..hlamy sdecemnari a(Conrad )Y, orktow nFormation L.e eCree kMine U, SG S25338 e, xterna vilew of lef tvalve .X 1 ;2 ,USNM 218893 ;3 ,USNM 218894 ;4 .USNM 218895 ;5 .US\M 218896 ;6 ,USNM 218897 ;7 ,USNM 218898 ;8 ,USNM 218899 ;9 ,USNM 218900. 10 (.Jilamy sdecemnari a(Conrad )Y,orktow nFormation L,e eCree kMine U, SNM 218897 U, SG S25338, resilia ilnsertion o flef tvalve X ,3. 'ersamus 1,3 I- \ii i ii. il view ol i i^Iii valve, X 1 , 1,1 NN\l I 890 I , 'l, l S\ \| 2 I 8902 2. I SWI 2 IK! 102 ,mliiii.il view nl i ifilii valve ,X I ■ I IS\\ l2 I8905 ,(Iiiis.i Iview n fa ituulalei lspecmien ,X I 5,6 Kvleina lv iew o lleit valve ,X I: 5 ,LISNM 2 I 8901; 0 ,I SNM 21K005. ('.hesapertr jneffersoniu sseptenanu (sSay Y),orktow Fnormatio nL,e Ceree Mk in eU,SC 2S5338 7 .K .Kxterna lview o flef tvalve .X 1 :7 ,USNM 218906 ;8 ,USNM 218907. Chesapecte nmadisomu (sSay )Y.orktow nFormation L.e Ceree Mk in eL.'SNM 21890 8U, SG 2S5338. cross-sectio no rfigh vtalv ea,bou mt idwa dyorsoventrall vX1,. Chesapecte njeffersomu septenanu (sSay )Y,orktow nFormation L.e Ceree Mk in eU, SG 2S5338 2:, USNM 218909 v, entra vl iew o farticulated specimen X. 1 ;3 L, 'SNM 218910 c, ross-section o fleft valv ea,bou mt idwa dyorsoventrall v1X,. C.hesapecte jneffersomu jseffersomu (sSay Y),orktow Fnormatio nL,e Ceree Mk in eU,SG 2S533 84:, USNM 218901 c, ross-section o frigh tvalve a, bou tmidwa \dorsoventrallv X ,1 5; U, SNM 2189 1I. externa lview o frigh tvalve ,X 1;6 ,USNM 218912 .externa lview o flef tvalve ,x 1. SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY PLAT E23 3 6 7,C,.hesapecte njeffersoniu septenariu (sSay )Y,orktow nFormation L,e Ceree Mk in eU, SNM 218910, USCS 25338 :1 ,externa lview o frigh tvalve ,X 1 ;2 ,interna lview 'o frigh tvalve ,X 1 ;3 ,rib at ventra lmargin o flef tvalve ,X 3 ;6 ,externa lview o flef tvalve ,X 1 ;7 ,interna lview o flef tvalve, 4 5C,.hesapecte jneffersoniu jseffersoniu (sSay Y),orktow 'Fiiormatio nL,e Ceree Mk in eU,SN M218913 USGS 25338 :4 ,externa lview 'o flef tvalve ,X 1 ;5 ,resilia linsertion o flef tvalve ,X 3. (.shesap ejecjtjenrs osmeputsenc externa vl iew o rfigh vt alve X, Chesapec tmenadison (iuSa sYy<), 3 e, xterna lview o flef tvalve >, portion X3, . PLAT E25 1-4 C.hesapecte nmadisoniu (sSay )Y,orktow nFormation L,e eCree kMine U, SNM 218917 U, SG S25338. right valve :1 ,externa lview ,X 1 ;2 ,ornamentation ,X 3 ;3 ,interna lview ,X 1 ;4 ,resilia linser¬ tion X,3. 5(.Chesapecte njeffersoniu septenariu (sSay )Y,orktow nFormation L,e Ceree Mk in eU, SNM 218910. LISG S25338 d, orsa vliew o af rticulate dspecimen X,1. 6 C.hesapecte nmadisoniu (sSay )Y,orktow nFormation L,e eCree kMine U, SNM 218918 U, SG S25338. externa vl iew o flef tvalve X. 1. teroventr seiupstenc n avlie wo SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY y.-yvvu-v Chesapec lceonccyme l(uDsa Pli)u,n gRoiver Le eCree kMine U, SG S2533H I )L'SNM 21B922 ,right valve :I ,externa lview ,X 1.4 ;2 ,interna lview rtenolium ,X 3 ;1 ,libs in mid-par to frigh tvalve ,X 3. 5 ISW1 21H923 ,externa lview o lpartia lvalve ,X 1.3. h lS\M 2IK924 ,ribs in anteroventra lportion o frigh tvalve ,X 3. kk SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY ('.hesapert ecnoccymel u(Dsa lCi)a. lve Frotrmatio In’l,u Pmoi nMt,aryland ( =(lltlamy L(fyropecten m) adisontu shassle rtIi cket-Rowland )h, olotyp e IlS, NM 4I591 9 JIS. (> S2447 l<4 ivalve :I ,externa lview ,X 1.5 ;2 ,dorsa lportion ,X 3 ;3 ,ventra lportion ,x 3. ISNM 2IK927 . IS(.S 24345 ,externa lview o lrigh tvalve ,X 2. Holotype ,ISNM K7754 ,externa lview o lef tvalve ,X 2. SMITHSONIA NCONTRIBUTION TS OPALEOBIOLOGY r/T A J.l yffg ffiM Gibson, Thomas G. 1987. "Miocene and Pliocene Pectinidae (Bivalvia) from the Lee Creek Mine and Adjacent Areas." Geology and paleontology of the Lee Creek Mine, North Carolina 61, 31–112. View This Item Online: https://www.biodiversitylibrary.org/item/266428 Permalink: https://www.biodiversitylibrary.org/partpdf/352106 Holding Institution Smithsonian Libraries Sponsored by Smithsonian Institution Copyright & Reuse Copyright Status: In copyright. Digitized with the permission of the rights holder. Rights Holder: Smithsonian Institution License: http://creativecommons.org/licenses/by-nc-sa/4.0/ Rights: http://biodiversitylibrary.org/permissions This document was created from content at the Biodiversity Heritage Library, the world's largest open access digital library for biodiversity literature and archives. Visit BHL at https://www.biodiversitylibrary.org. 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