A CONTRIBUTION TO OUR KNOWLEDGE OF THEANATOMY OF THE FRESH-WATER MUSSELS OF THEDISTRICT OF COLUMBIA
By Lucy Reardon0/ Washingto?i, District of Columbia
All of the North American fresh-water mussels are contained inthe family Unionidae, of which five genera are native to the Districtof Columbia. These are Lampsilis, Sirophitus, Anodonta, Alasmi-donta, and EUiptio. The genus Lampsilis has four species native tothe District of Columbia
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L. cariosus Say,i. ochraceus Say,i. radiatusGmelin, and L. nasutus Say. StropMtus has one local species :/S.undulatus Say. Anodonta has one: A. cataracta Say. Alasmidontahas three: A. undulata Say, J.. Tieterodon Lea, and A. marginata Say.EUiptio is represented by two local species : E. complanatus (Solander)Dillwyn and E. productus Conrad.In the following "Anatomical descriptions are given the differencesexhibited by five local species, namely, Lampsilis ochraceus, L. nasu-tus, Anodonta cataracta, EUiptio complanatus, and E. productus.ANATOMY OF LAMPSILIS OCHRACEUS SAYPlate 1, figs. 1 to 10DESCHIPTION OF THE SHELLPlate 1, figs. 1, 2, and 4The shell is elliptical with full beaks which are sculptured with afew straight, stout ridges. Posteriorly from the beaks a well-devel-oped posterior ridge begins and curving slightly down the middle ofthe shell ends in a blunt point halfway up the height of the shell.The outside is dull, tawny-brownish, usually smoky and feebly rayed.The interior of the shell is pearly gray, iridescent, often growinginto a deep rose along the margin of the shell.The left valve has two small pseudocardinal teeth in front of thebeak cavities and two thin, lateral hinge teeth. The right valve hastwo pseudocardinals opposite each other (with a pit between) andone high thin lateral.No. 2782.?Proceedings U. S. National Museum, Vol. 75, Art. M27800?29 1
%2 PEOCEEDINGS OF THE NATIONAL MUSEUM vol.75The muscle scars of both shells are identical, forming shallow cica-trices on the interior face of the shell. The anterior adductor scarlies in front of the pseudocai'dinal teeth and is somewhat oval inoutline. At the termination of the lower pseudocardinal tooth isthe anterior retractor muscle scar which is deeper than the anterioradductor scar and continuous with it. Below the impression ofthese two muscles is the small circular impression of the protractorpedis muscle. At the termination of the lateral hinge tooth is thescarcely visible oval scar of the posterior adductor muscle. Directlyabove it is the impression of the posterior retractor muscle which issmall and circular and often invisible. A very faint line runs abouta quarter of an inch from the margin of the shell from the anteriorto the posterior adductor muscle. It is the impression of the pallialline muscles, small muscles inserted along the margin of the mantle.In the beak cavities there is an irregular number of very smallscars, one of which is a deep elliptical scar in the apex of the cavityand is the impression of a small dorsal mantle muscle.UANTLEPlate 1, fig. 3The mantle lobes are separated for almost the length of the poste-rior adductor muscle in the formation of the dorsal mantle aperture.They are then united for about 3 mm. before separating to form theexhalent siphon. The tentacles of the exhalenl siphon are rudi-mentary while those of the inhalent siphon are from 1 to 2 mm. inlength.The pigmentation of the dorsal mantle aperture and of the siphonis heavy, growing fainter and disappearing as the margins continueanteriorly.The lack of pigmentation along the entire mantle edge, exclusive^of the siphons, the absence of tentacles beyond the inhalent siphonbut rudimentary tentacles at the exhalent siphon and a more elon-gate form of body distinguish this species from L. nasutus.MUSCULAR SYSTEMPlate 1, fig. 8The largest muscles are the anterior and the posterior adductormuscles, great cylindrical masses of fibers situated on a line witheach other on the dorsal portion of the body, piercing the mantle asthey traverse the body to their attachment on the valves. Theirfunctioning keeps the valves closed.The remaining muscles are the anterior and the posterior retrac-tors, the protractor pedis, two small muscles inserted in the cavitiesof the beak, and the small muscles of the pallial line. In alcoholicspecimens, the anterior retractor muscle is very small and circularin appearance, with its point of insertion just posterior to the upper
ABT. 11 ANATOMY OF FRESH-WATER MUSSELS REARDON 3portion of the anterior adductor muscle. This muscle passes down-ward to the anterior ventral portion of the foot with its greatestdevelopment in the anterior portion.The posterior retractor muscle lies on the anterior ventral portionof the posterior adductor muscle. At this point it is a compactcylinder of fibers which after a short distance spreads diagonally-through the body and foot and supplies the thick musculature of thefoot. These muscles are antagonistic to the protractor pedis musclewhich lies just at the base of the anterior adductor muscle and pre-sents, with the mantle intact, a crescent-shaped form. With themantle removed, it is seen to be fan-shaped, spreading outward overa large portion of the body and foot. By its play the foot is capableof great expansion. The two small muscles with their attachmentsin the beak cavities serve to ret'ain there the dorsal portion of thebody. The pallial line muscles are inserted along the edge of themantle and form a delicate connection between the mantle and shell.The muscular system of the remaining species is the same as forL. ochraceus. LABIAL PALPSPlate 1, fig. 7The labial palps surround the mouth and consist of two pairs ofthin contractile flaps which are subtriangular in shape with an innerand outer palp on each side of the body. Their edges are attacheddorsally and are free ventrally. The outer edge of the outer palp isattached to the mantle, with the inner edges of each palp united, andthe outer edge of the inner palp attached to the body mass. Ante-riorly the palps are attenuated and at their confluence directly underthe anterior adductor muscle give contour to the oral orifice with theattenuated portion of the outer palp forming the upper lip and thatof the inner palp forming the lower lip.The exterior faces of the palps are smooth. The inner faces arestrongly furrowed transverselj^ for about three-quarters of the dis-tance, where the transverse furrows terminate abruptly and longitu-dinal furrows begin and continue to the mouth where they curveinward and pass into the gullet. These ridges bear cilia which sweepalong the food brought into the mantle cavity at the inhalent siphons.The cilia on the transverse ridges check undesirable substances andsend them back into the mantle cavity, while the cilia of the longi-tudinal furrows sweep the desirable food into the mouth.GILL3 AND KEPRODUCTIVK SYSTEMPlate 1, figs. 6, 7, and 9The noticeably semicircular form is the only peculiarity of thegills of L. ochraceus. The marsupium occupies the hinder portionof the outer gills.The ^lochidia are bookless.
4 PROCEEDINGS OF THE NATIONAL MUSEUM vol.75BEAK SCULPTUREPlate 1, fig. 5 JALIMENTARY SYSTEM . 1Plate 1, fig. 9The mouth is immediately below the anterior adductor muscle.It is oval in shape and leads by a short gullet into the stomach, whichis of irregular shape, but more oval than globular, with plications onits inner surface, and lies just posterior to the anterior adductormuscle. Surrounding the stomach are the digestive glands, hepato-pancreas, a brown, spongy mass made up of minute tubes in clusterswhose orifices open into the stomach. The intestme is given off fromthe left posterior portion of the stomach and, in alcoholic specimens,is about 3 mm. in diameter. It descends obliquely through thevisceral mass with a slight curve almost to the posterior margin ofthe foot where it curves dorsally following the line of the foot margin-It is narrowest here, about 1 mm. in diameter. At a point midwaybetween the dorsal and ventral portions of the body mass the curveproceeds anteriorly and continues in an oblique line until at a pointbelow the anterior portion of the renal organ it turns to the rightand then backward, still following the curve of the foot, and contin-ues anteriorly for about two-thirds of the length of the body whereit is attached to the visceral mass. Turning again to the right sideof the body, it continues dorsally and posteriorly, keeping to the rightof the portion descending from the stomach. It continues anteriorlyfor a short distance where it again turns and passing upward becomesvery broad?about 5 mm. in diameter. From this point the wall isproduced into a fold (typhlosole) continuing through the rectum.Approaching the dorsal surface in an oblique line it grows graduallysmaller until it turns abruptly backward and passes into the pericar-dium; leaving the visceral mass, the intestine or rectum passesthrough the heart over the posterior adductor muscle, and bendingdorsally terminates with the anus in the suprabranchial chamber.The labial palps and alimentary system are the same for all species.NERVOUS SYSTEMPlate 1, fig. 10Paired nerve centers or ganglia, with their emanating branches andcommissural cords connecting the ganglia, form the nervous system.There are three nerve centers, an anterior, a visceral, and a posterior,supplying the respective portions of the body, which are called thecerebral ganglia, the pedal ganglia, and the posterior ganglia.The cerebral [ganglia are paired and lie bilaterally symmetricallyon each side]pf the^body in front of the protractor pedis muscle.
ART. 11 Aiq-ATOMY OF FRESH-WATER MUSSELS REARDON 5They are very near the surface, being exposed by removing the filmof the mantle. A single ganglion is roughly triangular with the apexdirected downward and a little anteriorly. From the most anteriorend there is a stout cerebral commissure which passes over the gulletto connect with the ganglion of the other side. From the anteriorventral portion three large nerves arise. The most anterior onebifurcates after a short distance, one branch passing around the mostanterior edge of the mantle and the other descending to the anteriorportion of the mantle. Behind this nerve descends another, also bifur-cating after a short distance and supplying also the anterior mantlearea. The last of these three nerves, after bifurcating, divides andredivides to supply the remaining anterior portion of the mantle. Atthe middle anterior portion of this ganglion a nerve arises which passesto the anterior adductor muscle, supplying it with its branches.Posteriorly the ganglion narrows to pass into the posterior commis-sural cord which passes upward through the visceral mass into therenal organ where it runs parallel with the commissural cord of theopposite ganglion. After leaving the renal organ the two commis-sures spread out to pass around the tendons of the posterior retractormuscle, after which for a short distance they run close together andpass into the posterior ganglion. From the inward central portionof the cerebral ganglia the pedal commissural cord arises at rightangles, then turns abruptly down, passes through the protractor pedismuscle, and descends deep into the center of the foot to meet the pedalganglion. On the dorsal portion of the cerebral ganglion are twovery small nerves which supply the protractor pedis and the anteriorretractor muscle. The labial palps receive a filamentous nervesupply from a branch of the anterior mantle nerve.The pedal ganglia lie at a slight^ elevated angle deep in theventral part of the visceral mass near the center. They are exactlycontiguous and present a bilobed appearance, though they are notfused.At the anterior end the stout commissural cord to the cerebralganglion arises. From the posterior end two large nerves are givenoff. The inner, after bifurcating, traverses the whole length ofthe body mass. The outer nerve bifurcates, sending its branches,which also fork, to the muscles of the foot. On the outer edgeof the ganglion two forking nerves arise and continue to themusculature of the foot. From the inward portion of the ganglionat the center a nerve arises at right angles and supplies the viscera.At the posterior nerve center the paired ganglia have becomefused into a single bilobate mass which is situated on the ventralsurface of the posterior adductor muscle. From the anterior endfour nerves pass. The two inner or mesial ones are the commissural
6 PROCEEDINGS OF THE NATIONAL MUSEUM vol.75
cords which pass to the cerebral gangha. The two outer ones passparallel for a short distance with the commissural cords and thenturning abruptly backward continue along the junction of the gillssupplying them with its numerous branches. At the posterior por-tion a gigantic nerve arises which separates into three large branches.The central branch supplies the inhalent siphon, the inner or mesialbranch the posterior portion of the mantle, and the outer branch theexhalent siphon.The nerves emanating from the ganglion often vary with theindividual mussel. A certain nerve may be entirely lacking orexceedingly large or very delicate. The most constant arrangementhowever, is the one given above and shows no variation for differentspecies. 'EXCRETORY SYSTEMPlate 1, fig. 9The excretory system for all five species exhibits no peculiarities.CIRCULATORY SYSTEMPlate 1, fig. 10The circulatory system of L. ochraceus and of the other speciesincluded in this study shows no variation. From the ventricle pro-ceed two aortae, one passing anteriorly and above the rectum, thoughalmost contiguous with it; the other passing posteriorly enters thevisceral mass below the rectum. They are the anterior and posterioraortae from which numerous arteries arise. The anterior aorta, onentering the visceral mass, curves outward and slightly to the right,then passes downward and a little posteriorly gives off a large artery,which passes into the mantle. The main branch continues its down-ward anterior course and near the center of the visceral mass dividesinto three large arteries which pass in and out among the folds of theintestine. Just before the curving main branch begins its downwardcourse a large artery is given off which curves downward back ofthe anterior adductor muscle and curves posteriorly, to supply, withits numerous veins, the ventral portion of the body mass. Fromthis artery, a little before it reaches the anterior adductor muscle,ascends a branch which passes into the muscle, supplies the mouthand anterior portions of the body.The posterior aorta bifurcates just before reaching the posterioradductor muscle, sending one branch to the muscle and to the regionof the pericardium and the rectum. The other branch passes overthe muscle and enters the mantle, continuing ventrally to meet theanterior mantle artery. The blood supply of the mantle is continu-ally oxygenated by the current of water which bathes the inner faceof the mantle. It is, therefore, returned directly to the auricleswithout passing through the gills.
AET. 11 ANATOMY OF FRESH-WATER MUSSELS REARDON" 7ANATOMY OF LAMPSILIS NASUTUS SAYPlate 2, figs. 1 to 10DESCRIPTION OF THE SHELLPlate 2, figs. 1, 2, 4The shell is not shiny and ranges in color from dark brown toolive green; it is thin to moderately solid, elongated, and has a dis-tinct posterior ridge, which generally is curved down the middle.The anterior ventral margin curves broadly to the base which is fullbehind the center, attenuating to a long point halfway up the heightof the shell. *The highly characteristic beaks are low and sculptured with fineclose ridges, looped in front and following the paralleling longitudinalaxis of the shell behind. (PI. 2, fig. 5.) The exterior surface showsirregular growth lines, with sometimes vertical bars just back of thecenter, representing the growth of the shell over the gills while dis-tended with fry. Young shells are finely rayed, while in the adultshell the rays are less distinct or entirely invisible.The interior of the shell is iridescent and lustrous and may bebluish-white, lurid, flesh-tinted, or purplish. The left valve has twopseudo cardinal teeth and one lateral hinge tooth, which is nearlystraight and very delicate. The right valve has one pseudocardinaltooth with a faint one above it and two lateral hinge teeth. Themuscle scars are shallow, the anterior adductor scar being the moreprominent. It is situated dorsally near the anterior margin of theshell and is oval shaped and very clear cut. The posterior adductorscar is a large faint oval impression just below the termination ofthe hinge teeth. Dorsal to it is the small circular impression of theposterior retractor muscle. On the posterior ventral margin of theanterior adductor muscle scar are two small irregular impressions, onedorsal. They are the anterior retractor and the protractor pedismuscle scars, respectively. Beginning at the most ventral point ofthe anterior adductor muscle scar, there is a thin faint impressionrunning parallel with the margin of the shell and about one-fourthinch distant from it and ending at the base of the posterior adductormuscle. It is the pallial line impression and marks the insertion ofthe small pallial line muscles. There are two small pitted scars inthe beak cavities which mark the insertion of the small dorsalmuscles. MANTLEPlate 2, fig. 3From the posterior adductor muscle the margins of the mantle areseparated for the length of the muscle to form the dorsal mantleaperture. The edges reunite for a short distance and then separateagain to form the exhalent siphon, the lower portion of which is
8 PROCEEDINGS OF THE NATIONAL MUSEUM vol.75formed by the junction of the gills. It meets again, but is not fused,to form the upper part of the inhalent siphon and below this pointis not united. The margins of both siphons are greatly thickenedand pigmented, bearing on their inward surface numerous tentacles.In specimens preserved in alcohol the tentacles of the inhalent siphonhave an average length of 3 mm., while the tentacles of the exhalentsiphon are smaller and not so numerous. From the inhalent siphonthe tentacles continue on the inward margin of the mantle to amedian point, growing smaller and diminishing in number until thelast several tentacles are about 5 mm. apart. The margin from thispoint to its junction over the anterior adductor muscle diminishes inthickness and is free from tentacles. The edge of the mantle is dis-tinctly pigmented along its entire course. This pigmentation is veryheavy at the siphons and at the posterior tentacle-bearing portion.GILLS AND KEPRODUCTIVE SYSTEMPlate 2, figs. 6, 7, and 9The gills are elongated with the inner lamellae continuous withthe visceral mass anteriorly. There are about 10 gill filamentsbetween the septa of that portion of the gills which serves as a mar-supium and about 20 septa between that which does not, so that agill or a part of one with more numerous septa than other portionsis indicative of a marsupium and therefore of the female mussel.There is a very inconspicuous longitudinal furrow passing aroundthe base of the inner gills and is caused by a very slight invaginationof the gill filaments. The inner or mesial gills have no such groove,for the filaments are smoothly curved as they bend uponthemselves at the base. This furrow is present in the gills of bothsexes. In L. nasutus the gravid gill protrudes much beyond theoriginal base of the filaments. This condition is readily seen by theprojection of the bulging gills beyond the chitinous rods of the fila-ments which have a clear-cut line of termination. This projectionbeyond the filaments is not uniform, for the septa are continuouswith the stretched area, checking at their points of insertion thebulging, and therefore giving a scalloped or beaded appearance tothe edge of the gill.In L. nasutus the posterior portion of the outer gills is specializedto form the marsupium.The glochidia are of the bookless type.BEAK SCULPTUREPlate 2, fig. 5ANODONTA CATARACTA SayPlate 3, figs. 1 to 10In the genus Anodonta the male and female shells are alike, thebeak sculpture is coarse and the embryos fill the entire gills, forming
AKT. 11 ANATOMY OF FEESH-WATER MUSSELS REARDON 9smooth pads. The inner lamellae of the inner gills are free from thevisceral mass. Hinge teeth are absent and the muscle scars faint.The shell is rather thin, evenly rounded in front and somewhatbiangulate behind and is very slightly winged in the postero-dorsalregion. The beaks are rather full, the sculpture consisting of amoderate number of concentric ridges which are usually doublylooped. The surface is usually covered with irregular growth lines.The exterior is generally shining, greenish-yellow, yellow-green orolive, usually banded with darker color and often faintly rayed. Theinterior is bluish-white and not shining. There are no small, dorsalmuscles in Anodonta. MANTLEPlate 3, fig. 3The mantle edge is strongly pigmented at the siphons. Theconnection of the mantle edge runs nearly the length of the posterioradductor muscle, restricting the dorsal mantle aperture to a veryshort slit and causing it to lie behind the anterior adductor muscle.The tentacles of the inhalent siphon are large wdth some of themforking. The exhalent siphon has no tentacles.GILLS AND REPRODUCTIVE SYSTEMPlate 3, figs. 6, 7, and 9The gills are semicircular with the inner lamellae of the inner gillsfree from the visceral mass. The entire outer gill serves as a marsu-pium. During the breeding season the water tubes of the marsupiumare divided longitudinally into three tubes with the two outer tubesfacing the inner and outer lamina. It is only the central tube whichcontains embryos. This threefold division of the water tubes ispresent only during the breeding season.The glochidia oi A. cataracta are of the hooked type.BEAK SCULPTUREPlate 3, fig. 5Elliptio productus Conrad and Elliptio complanatus (Solander)Dilhvyn.In this genus three species of the fisherianus group, Elliptioproductus, E. Hslierianus, and E. lanceolatus have been thought tooccur in the District of Columbia. Close examination of both shelland morphology shows that there is no constant distinction, and it istherefore thought that the only representative of this, the JisJierianusgroup, in the District of Columbia is E. productus Conrad.The group of Jisherianus is distinctive in the manner of gill attach-ment, for the outer lamina of the inner gill, instead of having the usualconnection to the visceral mass, is free.
10 PEOCEEDINGS OF THE NATIONAL MUSEUM vol. 75ELLIPTIC COMPLANATUSPlate 4, figs. 1 to 10SHELLPlate 4, figs. 1, 2, and 4The shell of Elliptio complanatus has an elongate trapezoidal shape,with the dorsal and ventral margins nearly parallel. The posteriorridge which is well developed and generally double, ends in a point atthe base, while the anterior end is rounded.The surface of the shell is marked by irregular growth lines whichare smooth in the young shell and rough in the old. In color itranges from tawny green to greenish brown.In E. complanatus there is no marsupial bulge distinguishing thefemale shell. The interior may be white, straw-color, salmon, orvarious shades of purple.In the left valve there are two nearly straight lateral hinge teethand two irregular pseudocardinals, while in the right valve there isone lateral hinge tooth and one stumpy pseudocardinal with a faintone above it.From the base of the anterior adductor scar just in front of thepallial line impression, there is a delicate groove which passes down-ward and curves around the base of the shell representing thecourse of the mantle artery. MANTLEPlate 4, fig. 3The only variation in the mantle is a heavier pigmentation at thesiphons. The anterior and posterior adductor muscles are verylarge with the anterior muscle assuming a distinct quadrilateral shape.The body is roughly trapezoidal in shape.GILLS AND REPRODUCTIVE SYSTEMPlate 4, figs. 1, and 9The gills are semicircular with the marsupium occupying the entireouter gills.The glochidia are bookless.BEAK SCULPTUREPlate 4, fig. 5ELLIPTIC PRODUCTUSPlate 5, figs. 1 to 10SHELLPlate 5, figs. 1, 2, and 4The shell is elongated, ranging in color from dark reddish brownto olive green and is rather thin. The beaks, which in the adultshell are generally eroded, are low. In very young shells there is a
ART. 11 ANATOMY OF FRESH-WATER MUSSELS?REAEDON 11definite beak sculpture so characteristic that it is a reliable meansof classification. In E. produdus the beak sculpture consists ofstrong, longitudinal, corrugated ridges.The posterior ridge is well developed, curved down the middle,ending behind the center in a long, drawn-out point near the medianline with the point often turned up. From the beaks in a radialdirection are heavy, irregular growth lines.The interior of the shell is iridescent and is purplish or whitish andshows muscular scars. In the left valve on the dorsal surface aretwo stumpy pseudocardinal teeth and two strong lateral hinge teeth.In the right talve is one pseudocardinal and one lateral tooth.MANTLEPlate 5, fig. 3The mantle edge at the dorsal mantle aperture and the siphonsis pigmented, but not heavily so. The dorsal mantle apertureextends almost the length of the* posterior adductor muscle, whilethe connected portion between this aperture and the exhalentsiphon is about as long as the inhalent siphon. Both siphons beartentacles. The body is slender and elongate.GILLS AND REPRODUCTIVE SYSTEMPlate 5, figs. 6, 7, and 9The gills are very much elongated, with the outer pair serving as amarsupium and forming a smooth pad when filled with embryos.The glochidia are bookless.BEAK SCCLPTUREPlate 5, fig. 5EXPLANATION OF PLATESFigure 11. Hinge line. 5. Anterior end.2. Beaks. 6. Posterior end.3. Growth lines. 7. Ventral margin.4. Dorsal margin. Figure 21. Lateral hinge teeth. 5. Anterior retractor muscle scar.2. Posterior retractor muscle scar. 6. Anterior adductor muscle scar.3. Posterior adductor muscle scar. 7. Protractor pedis muscle scar.4. Pseudocardinal tooth. 8. Pallial line muscles scar.Figure 31. Anterior retractor muscle. 9. Renal org'an.2. Anterior adductor muscle. 10. Posterior retractor muscle.3. Protractor pedis muscle. 11. Dorsal mantle aperture.4. Pallial line muscles. 12. Posterior adductor muscle.5. Foot. 13. Exhalent siphon.6. Pericardial gland. 14. Inhalent siphon.7. Ventricle. 15. Dorsalmantle muscles.>^. Left auricle.
12 PEOCEEDINGS OF THE N'ATIOITAL MUSEUM 1Figure 41. Pseudocardinal teeth.2. Anterior retractor muscle scar.3. Anterior adductor muscle scar.4. Protractor pedis muscle scar. 5. Pailial line muscles scar.6. Lateral hinge tooth.7. Posterior retractor muscle scar
.
8. Posterior adductor muscle scar.Figure 5
1. Cross section of shell.
1. Left mantle lobe.2. Labial palps.3. Foot.4. Outer gill.
Beak sculpture, enlarged.Figure 62-3. Glochidia, enlarged.Figure 75. Marsupium.6. Inner gill.7. Right mantle lobe.Figure 81. Anterior retractor muscle.2. Anterior adductor muscle.3. Protractor pedis muscle.4. Posterior retractor muscle.
1. Mouth.2. Stomach.3. Intestines.4. Typhlosole.5. Rectum.6. Anus.7. Hepato-pancreas.8. Gonads.
5. Posterior adductor muscle.6. Pailial line muscles.7. Dorsal mantle muscles.Figure 99. Renal aperture.10. Reno-pericardial aperture.11. Ventricle.12. Left auricle.13. Urinary bladder.14. Kidney.15. Pericardium.Figure 101. Cerebral ganglia.2. Anterior adductor muscle nerves.3. Cerebral commissure.4. Anterior mantle nerves.5. Pedal commissure.6. Pedal ganglion.7. Anterior visceral nerves.8. Anterior visceral nerves.9. Visceral nerves.10. Posterior visceral nerves.11. Posterior visceral nerves.12. Posterior commissure.13. Posterior ganglion.14. Posterior mantle nerves.
15. Gill nerves.16. Exhalent siphon nerves.17. Inhalent siphon nerves.18. Ventricle.19. Left auricle.20. Anterior aorta.21. Anterior adductor muscle artery.22. Pedal artery.23. Visceral artery.24. Posterior aorta.25. Posterior mantle artery.26. Posterior adductor muscle arterj'.27. Anterior mantle artery.
Plate 1Plate 2Plate 3
Lampsilis ochraceus Sa}'.Lampsilis nasutus Say.Anodonta cataracia Say. Pl.\te 4Elliptio complanatus (Solander) Dillwyn.Plate 5Elliptio productus Conrad. o
U. S. NATIONAL MUSEUM PROCEEDINGS, VOL. 75, ART. 11 PL. 1
Lampsilis ochraceus SayFor EXPLANATrON OF PLATE SEE PAGE )2
U. S. NATIONAL MUSEUM PROCEEDINGS, VOL. 75, ART. 11 PL. 2
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Lampsilis nasutus SayFor explanation of plate see page 12
U. S. NATIONAL MUSEUM PROCEEDINGS, VOL. 75, ART. 11 PL. 3
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Anodonta cataracta SayFor explanation of plate see page 12
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Elliptic complanatus iSolander) DillwynFor explanation of plate see page 12
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Elliptio productus ConradFor explanation of plate see page 12