Megaspores and a Palynomorph from the Lower Potomac Group in Virginia FRANCIS M. HUEBER i m SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY imr >? j f * " SERIES PUBLICATIONS OF THE SMITHSONIAN INSTITUTION Emphasis upon publication as a means of "diffusing knowledge" was expressed by the first Secretary of the Smithsonian. In his formal plan for the Institution, Joseph Henry outlined a program that included the following statement: " I t is proposed to publish a series of reports, giving an account of the new discoveries in science, and of the changes made from year to year in all branches of knowledge." This theme of basic research has been adhered to through the years by thousands of titles issued in series publications under the Smithsonian imprint, commencing with Smithsonian Contributions to Knowledge in 1848 and continuing with the following active series: Smithsonian Contributions to Anthropology Smithsonian Contributions to Astrophysics Smithsonian Contributions to Botany Smithsonian Contributions to the Earth Sciences Smithsonian Contributions to the Marine Sciences Smithsonian Contributions to Paleobiology Smithsonian Contributions to Zoology Smithsonian Studies in Air and Space Smithsonian Studies in History and Technology In these series, the Institution publishes small papers and full-scale monographs that report the research and collections of its various museums and bureaux or of professional colleagues in the world of science and scholarship. The publications are distributed by mailing lists to libraries, universities, and similar institutions throughout the world. Papers or monographs submitted for series publication are received by the Smithsonian Institution Press, subject to its own review for format and style, only through departments of the various Smithsonian museums or bureaux, where the manuscripts are given substantive review. Press requirements for manuscript and art preparation are outlined on the inside back cover. S. Dillon Ripley Secretary Smithsonian Institution S M I T H S O N I A N C O N T R I B U T I O N S T O P A L E O B I O L O G Y ? N U M B E R 49 Megaspores and a Palynomorph from the Lower Potomac Group in Virginia Francis M. Hueber SMITHSONIAN INSTITUTION PRESS City of Washington 1982 A B S T R A C T Hueber, Francis M. Megaspores and a Palynomorph from the Lower Potomac Group in Virginia. Smithsonian Contributions to Paleobiology, number 49, 69 pages, 1 figure, 24 plates, 1982.?A plant microfossil assemblage comprising seven species of megaspores; Verrutriletes carbunculus (Dijkstra) Potonie, Echitrdetes cf. E. lanatus (Dijkstra) Potonie, Erlansonisporites erlansonii (Miner) Potonie, Thyla- kosporites retiarius (Hughes) Potonie, Arcellites disciformis (Miner) Ellis and Tschudy, Arcellites cf. A. pyriformis (Dijkstra) Potter, and Paxillitriletes species Hall and Nicolson; two species of the microspore Crybelosporites Dettmann, C. striatus (Cookson and Dettmann) Dettmann adherent to specimens oi Arcellites disciformis, and Crybelosporites species adherent to specimens of Ech'itriletes cf. E. lanatus; and the palynomorph Dictyothylakos pesslerae Horst; is recorded from the Patuxent Formation, Potomac Group, Lower Cretaceous (Barremian- Aptian) in Virginia, USA. A preliminary analysis of the enclosing matrix for microspores and pollen has related the collection site closely to lowermost Zone I of the Potomac Group as described by Hickey and Doyle (1977). The megaspore assemblage supported by acceptance of the oldest possible date derived from the microspore and pollen analysis suggests correlation with the Barremian-Aptian horizons in the English Wealden, Lower Cretaceous, and specifically with the "Arcellites Flora" of Hughes. Megafossils comprising two seed cones belonging to the Pinaceae, Pityostrobus hueberi Robison and Miller and Pityostrobus virginiana Robison and Miller have been reported from the site. A fruit or cupule of Caytonia has been found along with numerous seeds, fern fragments, coniferous woods, and cycadopsid cuticles. This array of megafossils is not described or illustrated herein. A backswamp area of sedimentation and type of habitat is suggested on the basis of the lithofacies and generalized composition of the flora. The writer fully agrees with Tschudy (1976) as to the importance of searching for megaspores in continental Mesozoic rocks to aid in correlating and subdividing the deposits more effectively. OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded in the Institution's annual report, Smithsonian Year. SERIES COVER DESIGN: The trilobite Phacops rana Green. Library of Congress Cataloging in Publication Data Hueber, Francis M. Megaspores and a Palynomorph from the Lower Potomac Group in Virginia Smithsonian contributions to paleobiology ; no. 49 Bibliography: p. 1. Spores (Botany), Fossil. 2. Palynology. 3. Paleobotany?Cretaceous. 4. Paleobotany? Virginia. I. Title. II. Series. QE701.S56 no. 49 [QE996] 560s [561M3] 81-607852 AACR2 Contents Page Introduction 1 Locality 1 Materials and Methods 2 Acknowledgments 4 Systematics 4 Verrutriletes Potonie, 1956 4 Verrutriletes carbunculus (Dijkstra) Potonie 4 Echitriletes Potonie, 1956 5 Echitriletes cf. E. lanatus (Dijkstra) Potonie 5 Erlansonisporites Potonie, 1956 6 Erlansonisporites erlansonii (Miner) Potonie 6 Thylakosporites Potonie, 1956 7 Thylakosporites retiarius (Hughes) Potonie 7 Crybelosporites Dettmann, 1963 10 Crybelosporites striatus (Cookson and Dettmann) Dettmann 10 Crybelosporites species 11 Arcellites Miner, 1935 11 Arcellites disciformis (Miner) Ellis and Tschudy 11 Arcellites cf. A. pyriformis (Dijkstra) Potter 13 Paxillitriletes Hall and Nicolson, 1973 15 Paxillitriletes species 15 Dictyothylakos Horst, 1954 15 Dictyothylakos pesslerae Horst, 1954 15 Conclusions 17 Literature Cited 19 Plates 21 in Megaspores and a Palynomorph from the Lower Potomac Group in Virginia Francis M. Hueber Introduction The present study grew out of finding speci? mens of the megaspore species Arcellites disciformis (Miner) Ellis and Tschudy 1964 during a routine examination of a collection of fossil plants I made in 1973. My original interest in the collection centered on the woods and gymnosperm cones; however, the beauty of the megaspore diverted my attention and led me to research the literature for any records of its occurrence in the Cretaceous Potomac Group. The search was a very brief one. I found the summary paper for the genus by Ellis and Tschudy (1964), in which there is citation of the occurrence of the species in the Patuxent Formation based on a written communication from W. G. Chaloner. The occurrence repre? sented stratigraphically the earliest for the genus, but no subsequent photographic documentation was published. I had obtained only three specimens from my original preparation of the matrix. I mounted the best one for viewing by means of the scanning electron microscope. The results were excellent; however, the additional details of anatomy and morphology needed to fully substantiate the iden? tification of the species required more specimens. Francis M. Hueber, Department of Paleobiology, National Museum of National History, Smithsonian Institution, Washington, D. C. 20560. Preparation of three more samples of the matrix and careful search yielded 84 well-preserved spec? imens and 15 badly distorted ones. The even more significant results of those preparations was the accumulation of other species of megaspores in adequate numbers to form the basis for this expanded and hopefully more useful report. Tschudy in 1976 and in later conversation gave added inspiration regarding the significance of this small assemblage of megaspores. In addition, an analysis of a sample of the matrix for micro? spore and pollen content was made by J . A. Doyle, whose findings served as the key to the stratigraphic correlations discussed later herein. Tschudy (1976) was correct when he wrote: I am convinced that once megaspores have been routinely searched for in continental Mesozoic rocks they, and the smaller palynomorphs accompanying them, will provide for the stratigraphic subdivision of non-marine rocks as effec? tively as ammonites and baculites now serve to subdivide marine rock sequences. LOCALITY.?Stratum 2 to 2\ feet (60-76 cm) thick and undetermined areal extent, comprising lignitized logs and other plant debris enclosed in a medium gray clay, with irregularly distributed pockets of silt and medium to coarse sand grains. Exposed in 1973 during construction of new sec? tions of the road bed of Henry Shirley Memorial Highway, Alexandria City, Virginia, on the slope between Seminary Road and Richenbacher Av- SMITHSONIAN CONTRIBUTIONS TO P A L E O B I O L O G Y enue at Lat. 38?49'46" N, Long 77?07'07" W, 7.5' Alexandria Quadrangle. The locality is given USNM Locality No. 14252. Age is Lower Cretaceous (Barremian-Aptian), Potomac Group, Patuxent Formation, Lower Zone I of Hickey and Doyle (1977). MATERIALS AND METHODS.?The collection comprises lumps of clay and sandy clay matrix containing lignitized woods, cones, leaf fragments and a large array of seeds. Preparation of a small sample was made, immediately after the collec? tion was obtained, in order to evaluate the quality of the fossil material before the matrix became dry. Most of the larger plant fragments disinte? grate after drying, even if the matrix is allowed to dry slowly within its protective paper wrap? pings. The first specimens of the spore genus Arcellites were observed and notes made indicating the importance of documenting photographically the presence of the spores in the Potomac Group. The collection was stored until time for additional preparations was available. The matrix when fresh and moist was a me? dium gray color; however, on drying a noticeable change to dusky yellow took place. I suspect that the change was due to oxidation of finely divided pyrite that contributes significantly to the origi? nal gray color. An efflorescence of melanterite is present on most of the samples, which are now quite dry, and its presence as an oxidation by? product lends credence to the probable explana? tion of the color change of the matrix. The sand and silt grains, distributed in irregu? lar pockets throughout the clay, primarily are angular, transparent to translucent quartz. A small fraction of the silt grains are euhederal zircon, along with mineral fragments tentatively identified as ilmenite and garnet. No attempt was made to carry out a complete qualitative and quantitative analysis of the matrix. The matrix will gradually disintegrate when soaked in water for at least one week. Unfortu? nately, however, the plant fossils remain coated with clay particles and sand grains. Complete maceration of the matrix with subsequent free and clean release of the plant material was best accomplished with concentrated (48%) hydro? fluoric acid. Transparent, polystyrene, lidded containers, the type used for food storage, were used to hold the acid and matrix samples during maceration. A platform to support the matrix was constructed from plastic containers of the type used in mar? keting fruits such as strawberries. Polyester screen of standard 0.5 mm mesh was placed on top of the supporting platform and then the specimen of matrix. The container was filled with concen? trated (48%) hydrofluoric acid in sufficient quan? tity to cover the matrix sample. The chemical reaction was exothermic and it was necessary to keep the containers in a cold water bath during the early part of the maceration. The macerations and first washings were done in a chemical fume hood. After 18 to 24 hours the maceration was com? plete. The larger fragments of plant remains were left lying on the screen while the smaller particles settled through to the bottom of the container. The screen was slowly lifted from the container by holding opposing edges with large, long for? ceps. Particular care was taken to avoid disturb? ing the fossil plant fragments more than neces? sary. A one gallon polyethylene cylinder, filled with tap water and fitted with a plastic supportive platform positioned about one inch below the water surface, was close at hand. The screen and plant fragments were carefully lowered into the water and placed on the platform. After one hour the water in the container was siphoned off and discarded. The container was immediately re? filled with fresh tap water. This washing was repeated four times. Sediment at the bottom of the container was not removed during the siphon? ing process but saved to be combined later with the sediment that had settled through the screen during maceration. Additional washing of the larger plant fragments was accomplished by in? verting the supportive screen into a 0.5 mm mesh plastic sieve that was partially submerged in a constant-flow water bath set up in the laboratory sink. The plant fragments generally settled in a NUMBER 49 single area in the sieve but by sweeping the piece of supportive screen forcefully through the water and near the specimens they were eventually well separated from one another. Washing continued for five hours. The washed material was then distributed among large (14 cm) petri plates for sorting and picking of the specimens. The sediment in the maceration containers was treated differently from the coarse fraction. First the supernatant liquid was carefully decanted into another plastic container for subsequent dis? posal. The container holding the sediment was then filled with tap water, the filling being done forcefully in order to lift the sediment and dis? perse it. The sediment was allowed to settle com? pletely, until the wash water was clear. The water was decanted and forcefully replaced again. This process was repeated ten times. The washed ma? terial was distributed among several small, shal? low, white glass containers for sorting and picking the specimens. Sorting was done at X 20 magnification, using a binocular dissecting microscope. Picking was facilitated by using a dropper pipette or a small scoop-shaped piece of 0.25 mm mesh copper screen. Significant large fragments of plant ma? terial were sorted into storage vials filled with distilled water and the megaspores were placed in small petri plates. No further chemical treat? ment was given to the sorted materials except to include granules of thymol in order to prevent growth of bacteria and fungi. This measure is important because the fossil remains are attacked by bacteria within 24 hours and only a short while later by aquatic fungi. It should be noted that at least 40% of the Arcellites were found floating along the margin of the meniscus in the sieve frame or plastic wash containers. The spores were held in place by surface tension and capillary action of the water. Several specimens of Thylakosporites were also found under the same circumstances, including the tetrahedral tetrads of the species as described herein. I recommend that future workers pay particular attention to this peculiarity, otherwise many megaspores will be lost during the washing and decanting processes. After isolation, the megaspores were transferred to distilled water and then further cleaned by being transferred rapidly from the distilled water to 100% ethyl alcohol and back to distilled water. The micro-convection currents caused by the im? mersion of the spore in the water after immersion in the alcohol swept away all of the minute debris that still may have clung to the spore body. This process was repeated four times, ending with transfer of the spore into the alcohol bath. The transfers were facilitated by supporting the spore or several spores at a time on a scoop-shaped, 0.25 mm mesh, copper screen. This technique also works extremely Well for cleaning larger plant fragments. The spores were individually removed from the alcohol bath, air dried and gently dropped into a depression slide for storage. They were generically and specifically sorted at that time. Manipulation of the spores for mounting on cover slips was facilitated by using a single eyelash attached with acetate glue to a round toothpick. The tip of the hair is extremely finely pointed and when moistened with distilled water can be used to pick, move, and position spores at will. Circular coverslips were coated on one surface with a thin film of white glue (Elmer's brand) that was allowed to dry. The individual spore was picked up with the moistened hair. The moisture absorbed by the spore from the hair in turn served to moisten the surface of the glue when the spore was touched to it. Drying was rapid and the spore remained firmly attached. By this means spores and spore fragments can be oriented for scanning electron microscopy as il? lustrated in the specimens of Arcellites. Dissections of Arcellites illustrated herein were accomplished by sharpening the point of an insect pin into the form of a microknife blade. The spore was moistened slightly with distilled water and then cut open in order to reveal the Y-mark. The dissected specimens were air dried and mounted in the same manner as the whole spores. The coverslips with the spores were mounted SMITHSONIAN CONTRIBUTIONS TO P A L E O B I O L O G Y on aluminum stubs. The spores were sputter coated first with carbon and then with gold-pal? ladium. They were viewed and photographed using Cambridge Mark?IIA, Cambridge S4-10, and Coates and Welter 106B scanning electron microscopes. ACKNOWLEDGMENTS.?I am grateful to the work crew of the Shirley Highway project for alerting me to their discovery of the fossil plant horizon that resulted in saving a small portion of it for the national collections, to Mary-Jacque Mann and Susann Braden for their enthusiastic and skillful operation of the scanning electron microscopes and processing of the photographic negatives, to James P. Ferrigno for the photo? graphic prints used to illustrate this paper, to Dr. James A. Doyle for his analysis of the matrix for associated palynomorphs and his comments con? cerning the stratigraphic correlations, to Garland R. Upchurch, Jr., for a preparation containing a specimen of Arcellites disciformis from Lower Zone I at Dutch Gap Canal, Virginia, to William G. Chaloner for locality data concerning the occur? rence of Arcellites reported by Ellis and Tschudy from the Patuxent Formation, to Lawrence B. Isham for drawing the diagram in Figure 1, and to Robert H. Tschudy and Roberta Townsend for comments and critical reading of the manu? script. Systematics The descriptions of the seven megaspores and two microspore species presented herein are ar? ranged according to the morphologic system of classification proposed by Potonie (1956). The single specimen of Dictyothylakos pesslerae Horst, 1954 is treated as a species of uncertain affinities because its position within Potonie's orderly ar? rangement remains obscure. Anteturma Sporites Potonie, H., 1893 Turma Triletes (Reinsch, 1881) Dettmann, 1963 Subturma Azonotriletes Luber, 1935 Infraturma Apiculati (Bennie and Kidston, 1886) Potonie, 1956 Genus Verrutriletes Potonie, 1956 Verrutriletes carbunculus (Dijkstra, 1949) Genus Echitriletes Potonie, 1956 Echitriletes cf. E. lanatus (Dijkstra, 1951) Infraturma Muronati Potonie and Kremp, 1954 Genus Erlansonisporites Potonie, 1956 Erlansonisporites erlansonii (Miner, 1932) Infraturma Perinotriletes Erdtman, 1947 Genus Thylakosporites Potonie, 1956 Thylakosporites retiarius (Hughes, 1955) Genus Crybelosporites Dettmann, 1963 Crybelosporites striatus (Cookson and Dettmann, 1958) Crybelosporites species Subturma Pyrobolosporites Potonie, 1956 Genus Arcellites Miner, 1935 Arcellites disciformis (Miner, 1935) Arcellites cf. A. pyriformis (Dijkstra, 1951) Turma Barbates Madler, 1954 Genus Paxillitriletes Hall and Nicolson, 1973 Paxillitriletes species Uncertain Affinities Genus Dictyothylakos Horst, 1954 Dictyothylakos pesslerae Horst, 1954 Verrutriletes Potonie, 1956 Verrutriletes carbunculus (Dijkstra) Potonie PLATES 1-3 Triletes carbunculus Dijkstra, 1949:10, pl. I: fig. 12. Triletes cf. carbunculus Dijkstra, 1951:10, pl. 2: fig. 11. Verrutriletes carbunculus (Dijkstra).?Potonie, 1956:28, pl. 3: fig. 26. DESCRIPTION (from Dijkstra, 1949:22).? Shape spherical. Diameter 600-1000 /i (the mean being 820 H, 4 spores measured). Tri-radiate ridge conspicuous, 50 [i broad, 40 ju high, its length being ca. 0.6 of the radius of the spore. Arcuate ridges lacking or scarcely visible. Spore wall, inclusive of the tri-radiate ridges and with exception of the contact faces, covered with hemispherical, red translucent 5 - 30 /i broad objects. Some specimens have but a few of such objects, which lie single or are joined to small groups; on other specimens they have been united to great complexes. Spore wall 30-36 fi thick, dark brown. The description given by Dijkstra in 1951 for another specimen, but from the English Wealden, varies little from the original one as presented above. Potonie's description (1956:28), when he estab? lished the new combination, translates as follows: NUMBER 49 The type, ca. 940 /t, has been shown to me. Equator more or less round to slight triangular. The "carbuncles" adhere irregularly distributed on the dull exine like solidified, glob? ular, glassy, transluscent, red, liquid droplets. They look like outflowed resin, which becomes more conspicuous by the fact that they occur in groups, leave asymmetrical spaces and are of very variable sizes. The form may be only provisionally placed in the series here. Similar ones in Hughes' collection. REMARKS.?The two complete, although dis? torted, specimens and the fragment illustrated herein conform to the descriptions given by Dijk? stra and Potonie with exceptions of the breadth and height of the tri-radiate ridge and the thick? ness of the spore coat. The tri-radiate ridge, as clearly evident in Plate 1 (figures 1, 2, and 4), is 28 jum broad and a 21 jum high, just over one- half the dimensions given for the type specimen. The thickness of the spore coats illustrated in vertical section in Plate 2 (figures 1 and 3) and Plate 3 (figure 2) is 15 /mi and 32 jum respectively. These exceptions cannot be attributed totally to shrinkage of the spores during dehydration by reason that the dimensions of the spore bodies are well within the range of size given in the descrip? tion of the type. The dimensions of the tri-radiate ridge, I feel, do not have so much significance as to be critical in species determination. The thin? ness of the spore coat of the fragment shown in Plate 1 (figure 6), which serves as the source for the photographs in Plate 2 (figures 1-3), is prob? ably attributable to corrosion and degradation of the wall following fragmentation of the spore. Its more porous structure is in obvious contrast to the dense structure of the spore coats of the complete but distorted spores shown in Plate 1 (figures 1-5) and Plate 3 (figures 1 and 2). The specific epithet, carbunculus, is exceptionally appropriate. Viewed through a binocular micro? scope at magnifications of 40 to 60 diameters, the spores seem encrusted over most of their surfaces with minute, lustrous, ruby cabochons. The or? namentations, best defined morphologically as gemmae (Plate 1: figure 3), are not present on the contact areas (Plate 1: figures 1 and 2; Plate 2: figure 4; Plate 3: figure 1). They are greatly reduced in size and number or are altogether absent on the distal surface of the spore body (Plate 2: figure 5). Potonie's allusion to them as resin that had flowed out onto the spore surface is appropriate. The gemmae appear to have been exuded from within the spore as a resinous sub? stance, retaining its glossy surface and viscous appearance after solidifying (Plate 1: figures 3 and particularly 5; Plate 2: figures 1 and 2). Structurally there is a smooth, thin film covering a foam-like inner layer (Plate 3: figures 2 and 4), the whole of which is subtended by a papilla of the outer exoexine (Plate 2: figure 2, papilla at arrow; Plate 3: figure 2). Viewed from the interior of the spore, in this instance the partially de? graded spore wall fragment (Plate 2: figure 3), a depression marks the position of a gemma on the outer surface. This characteristic cannot be seen when the endexine is intact (Plate 2: figure 6). Circular holes in the thin film covering the foam? like inner layer of the gemmae is a common feature seen on the spores that have been partially eroded (Plate 2: figure 7). OCCURRENCES.?Boring Sm. Maurits No. 554, South Limburg, Netherlands; Upper Cretaceous (Aachenian (Senonian)); Dijkstra, 1949. Epen and Vaals, South Limburg, Netherlands; Upper Cretaceous (Aachenian (Senonian)); Dijk? stra, 1949. Bore, D'Arcy Expl. Co. Kingsclere No. 1, 466: Weald, southern England; Lower Cretaceous (Barremian-Aptian); Dijkstra, 1951. This report, USNM Locality No. 14252, Pa- tuxent Formation, Potomac Group; Lower Cre? taceous (Barremian-Aptian). SPECIMENS.?GG-7A, USNM 304311; GG-7B, USNM 304312; GG-7C, USNM 304313. Echitriletes Potonie, 1956 Echitriletes cf. E. lanatus (Dijkstra) Potonie PLATES 4, 5 Triletes lanatus Dijkstra, 1951:11, pl. 2: fig. 22. Echitriletes lanatus (Dijkstra).?Potonie 1956:36, pl. 4: fig. 36. DESCRIPTION (from Dijkstra, 1951:11).? SMITHSONIAN CONTRIBUTIONS TO P A L E O B I O L O G Y Spore hemispherical, top area flattened. Diameter 600-800 ju. (the mean being 700 fx, 4 specimens measured). Tri-radiate ridges nearly as long as the spore radius, 20-30 fx broad, 50- 100 fx high. Arcuate ridge not clearly distinguishable. Spore coat covered with 10 ju, large papillae bearing hair-like wooly appendages, 150 ju long, 3-5 ju thick. Spore coat brown, 25 (X thick. Potonie (1956:36) described the species as fol? lows: Genotype around 780 fx (from the illustration); trilete, simple megaspores, equator subtriangular to circular, trilete rays not always present, exine ornamented on all sides with capilli to spinae, in the genotype provided with rounded verrucae, which subtend more or less long, hair-like, contorted capilli, otherwise with simple or hook-like spinae (translated by author). REMARKS.?Morphologically the two speci? mens illustrated herein conform to the descrip? tions given for the species, with the exceptions of the density of the capilli on the specimens (Plate 4: figures 1,2; Plate 5: figures 1, 3) and the low or poorly developed tri-radiate ridges. Accurate measurements of the spore body are precluded by the density of the capilli. Measurements exclud? ing the capilli can be estimated as low as 800 jum or, including the capilli, can be obtained as high as 1066 jum. These dimensions exceed the range given for the type specimen. I am assuming that the measurements of the type specimen did not include the capilli, that is, the dimension was of the spore body alone. If, however, one were to add the given length of the capilli, 150 jum, to the diameter of the spore body, 780 jum, the total of 930 jum would then fall within the measurable size given for the two specimens at hand. The specimens in this report are larger, but not so much so as to be excluded from the species. The capilli, which range from 65 to 135 jum long, are proximally broadened, in which case it could be interpreted that they are subtended by verrucae (Plate 4: figures 3, 4). Their apices are either pointed or simply to several times divided (Plate 5: figure 4). This latter character is not described for the type-species; however, most of the forked apices, because of their fragility, can be easily broken off during processing and thus are not readily observed (Plate 5: figure 3). A finely reticulate pattern can be seen as char? acteristic of the outer exoexine between the bases of the capilli (Plate 4: figure 4; Plate 5: figure 2). I have only two specimens of this megaspore and although their morphological differences from the type-species are probably significant enough to establish a new species, I prefer to designate them as E. cf. E. lanatus. Acquisition of additional specimens will permit more significant analysis of the similarities and differences than is possible at this time. Commonly, in both speci? mens, microspores, herein assumed to be related to this species, are found among the matted cap? illi. They are all of the same morphology and dimensions (Plate 4: figures 5, 6; Plate 5: figures 5, 6). Description of these microspores appears later, where they are assigned to Crybelosporites Dettmann, 1963 as Crybelosporites species. OCCURRENCES.?Boring B; Bore, D'Arcy Expl. Co. Kingsclere No. 1 at 706 feet and (?) 466 feet, Weald, southern England; Lower Cretaceous (Barremian-Aptian); Dijkstra, 1951. This report, USNM Locality No. 14252, Pa- tuxent Formation, Potomac Group, Lower Cre? taceous (Barremian-Aptian). SPECIMENS.?HH-1 A, USNM 304314; HH-1B, USNM 304315. Erlansonisporites Potonie, 1956 Erlansonisporites erlansonii (Miner) Potonie PLATE 6 Selaginellites erlansonii Miner, 1932:500, fig. 1. Erlansonisporites erlansonii (Miner).?Potonie, 1956:46, pl. 5: fig. 53. DESCRIPTION (from Miner, 1932:500).? Body of exine round, 465-1000 fx in diameter the mean being 690 fx; exine reticulate with irregular diaphanous appendages, 17-122 (x in width, giving the spore a total diameter of 500-1,155 fx with the mean at 790 ju; no com- misural ridges or clefts visible. Potonie (1956:47) describes the species as fol? lows: Genotype apart from the membranes of the muri 899 ju NUMBER 49 (from the photograph); equator circular, trilete mark not or poorly discernible probably because of the heavy reticula? tion. The muri of the reticulum merge into filmy lamellae that may be uniformly developed on the entire exine, how? ever, in the photograph of the genotype they become visible chiefly on the periphery of the spore (translated by the author). REMARKS.?One spore from among five speci? mens that were obtained from the prepared sam? ples is shown in Plate 6 (figures 1-6). It is 800 jum in diameter and is representative in form and structure of all of the specimens. The size range of the five specimens is 695 to 840 jum in diameter. The location and general size of the trilete mark is visible (Plate 6: figure 1), probably because of increased height of the muri of the reticulum along the leasurae instead of an extension of lips along the laesurate margins. Support for this observation requires microtome preparations and such are not within the scope of this report. The muri range from 14 to 45 jum in height between the bastion prongs, the prongs reaching as much as 78 jum in height. The outer exoexine is psilate (Plate 6: figure 4). Bastion prongs and the diaphanous muri con? necting them are quite obvious in Plate 6 (figures 1-3, 5). Sculpture of the muri is reticulate with minute, a 1.5 jum, clavae rising from the intersec? tions of the muri of the reticulum (Plate 6: figure 6). A precious opal-like iridescence of the spore coat is a notable characteristic of the species. Structural details of the spore coat relevant to this phenomenon were not obtained; however, I shall presume that they are identical to those described and discussed for Thylakosporites retiarius (Hughes) Potonie, the next species in this report. In that discussion it will be noted that the spore coat structure of this species and T. retiarius is compared to that of the two modern species of Selaginella. This evidence strongly suggests that it would be appropriate to return E. erlansonii to the original taxon Selaginellites, as proposed by Miner in 1932. However, the transfer will not be made herein because neither isotype material from Miner's collection nor additional specimens from the site described herein have been obtained for direct comparison and confirmation. OCCURRENCES.?Skansen, east of Disko Island, Greenland; Upper Cretaceous (?Campanian); Miner, 1932. This report, USNM Locality No. 14252, Pa- tuxent Formation, Potomac Group; Lower Cre? taceous (Barremian-Aptian). SPECIMENS.?GG-1 OB, USNM 304316; depres? sion slide with four unmounted specimens, USNM 304317. Thylakosporites Potonie, 1956 Thylakosporites retiarius (Hughes) Potonie PLATES 7-10 Triletes retiarius Hughes, 1955:213, pl. 11: figs. 3, 4. Thylakosporites retiarius (Hughes).?Potonie, 1956:49, figs. 5 5 - 57 [not 57 in text. Type-specimen not designated. Lecto? type designated by Jansonius and Hills, 1976, fig. 3 of Hughes.] DESCRIPTION (from Hughes, 1955:213).? Trilete megaspore probably spherical but the whole upper (apical) surface may be preserved infolded [figure citation]. Diameter 520-700 [X (mean 620 JU, 6 specimens). Tri-radiate ridges 200 /x long, 10 JU, broad, and 30 jti high; contact faces smooth except in one specimen where the perispore covers the whole spore surface. Distal hemisphere entirely covered [figure citation] with a mesh-like (net) perispore sometimes in different layers of different mesh size. The chief mesh strands are 15-35 /i wide and 10 fx thick [figure citation] but may also be circular in cross-section exactly as described and figured by Horst (1954) and figured by Michael (1936). Spore coat is brown but shows a red luminous effect in places; thickness of exoexine 15 fx, intexine very thin 2-3 /x and continuous with tri-radiate lips. Potonie (1956:49) gives an abbreviated descrip? tion that translates as follows: Genotype ca. 650 JU, (from the illustration), trilete mega? spore, probably spherical, however the entire proximal hem? isphere can be strongly folded, Y-radii extending nearly to the equator; exine smooth, however always surrounded on the whole distal side, in one specimen of the genotype also on the proximal side, by a perispore. The latter consists of an often multilayered reticulum [figure citation] similar to that which is described by Horst 1954, page 610, as Dictyo- 8 SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY thylakos pesslerae. Dictyothylakos is found in the German Weal- den coals of southern Mecklenburg and Odenwald. It was correct not to equate Dictyothylakos and Thylakos? porites because there could be other spore genera that have