hescesuaee said beateoeetsscretla series phere nde ty eeiseas libsateatla event iat Rares dpses tet mie sian reabse Eitri teibrrest eerie, cia rete ea: tad) Siete sare } Sota nas a —— “2 jutegaeen penetra neice eee oonet Seaeincmietis ie ptt cea — ery ae hen pairs st rae : eae Eaiseorpeee en f sly peseeriea it 4 Seer =) paths eeetion! a: nett pecan peeree ete seein pares nah - cent Scena cigs es Sees Ther crane a ee tit eahiee: 4 rm rate jet gesaeregney see Sst bepcatotyeeary span snsdepasath lignes hehe Seber vere be nen phe roraeatte Jiri aa th Beet = : et — een . ta aa : ot : # ate = oe ates cota a - Sihaaee th x: Beitr sha a et arte aso nie a hat se oneal Re rosto eyteiststans hs eos nd vet mart setae ee = tee Bunreac ater eee = sirens est peri rstaenes rat mietenoye arareterss Birt te fresarsstsy Batt ! Saag Fiat aa : ‘ vo : — +2 hae seeeat pace areneelctte ties on oer iataeseeerneaeaet ates Sere hfearecectgl rarity pts Shi na aS Sictess Sept eps ip india ai cua stahyn wes Eatscmeccim er ae a serapalneedaes ‘ sree ea st ceteris: “3 " sds nips egaegceskats (prt tc band boys net ier: oes Selewtsheetiesreleisnes See aaa Litbagste rte tutte ne inne nse tet Patckaan ape iteraesbanecaigetceialcet ify sehen asotsh iis pots mitts Ss jevelaquabitie stitr tare! is mati Sante eae = Sissy TRIS SRLOL NDIA tenet tach ii re taper cater cr er ee te ak at oa arte ioe chive! ee sive Tlie effete ae driaeeg gill yee See ae ss peaxeiacet nents LS rts ia ati earesyaetigens, £rh3 ne dee) “yt i ity ‘5 rience E sat i ie es: hs gehecticr eines Se iy +. Sasi eae pee sek Pear ea 4 ta Hate Steet pee sta] Mysly eeew satel niet cbest te setts ey rabies metic hart ee sie "ia site pemieq aie] y eeekee pein 41 te be epee abe : i te ney nee A Soir a een ie ies: sii scents aa ul pretest isehe pats Patenne tata tee getty pogeetont Stasi are) apepeekn ees pruanfavessean bot ete mle i ii leseenl * RSG es pen 2 Soe emcee ie iSesesisar inion " a eee ety et wastes tea a het iat aceasta ESE Te at ; it pee te tt Wigtiaamepsiteastam ieee erstttts eae Ft 2 eee nt Pore Tabi ae eS oes oa rae ie pues sibtiinctetses gs Ua ii moe lite Red er aetna ae aout raicoe aan pape ead ; sie Honene mates: Pee teetsttes ue ie byte appease’ ete erates jSiuneoe) f ae Serene oe raisers Patter seeeisanertstanessh shat repens syed os pha darian nee rile oe it ies Seeks Seas i isaaa irare gu gugann a Nepentorbrttel CU Seer TAL radgststs Tatts seaeti scan eat PALAEONTOGRAPHICA AMERICANA 1916-1929 ITHACA CONTENTS OF VOLUME I NUMBER lies ATLANTIC SLOPE ARCAS . By P. G. Sheldon THE GENERA LUTRETIA AND ALVEINUS ; developed in America . By G. D. Harris THE RUDISTIDS OF TRINIDAD : By G, D. Harris and F. Hodson especially as THE RECENT ARCAS OF THE PANAMIC PROVINCE By €. J. Maury THE VENERIDAE OF EASTERN AMERICA Recent ; F : By K. VAN WINKLE PALMER Cenozoic and PLATES | ae iy 17 18 - 28 29 - 31 32-6 PAGES ee 105 - (18 163 - 208 209 - 522 eee, en Fee | it iy) may rath we wf is " , % : ' 7 Ci oh : my, Ca pare 1 pi if ie : yt wih Neath ; ae ‘i is Wig . ft F F ' , i) elon ot a Lit 7 Al ,are © ey Aw ie ¢ : : 2 a . Ul if PALAONTOGRAPHICA AMERICANA ILLUSTRATED CONTRIBUTIONS TO THE INVERTEBRATE PALEONTOLOGY OF AMERICA No. I—Atlantic Slope Arcas By PEARL G. SHELDON ec ITHACA HARRIS COMPANY 1916 uy rive AG EVERAL years ago we commenced a series of papers in ‘‘Bulletins of American Paleontology,’’ dealing with the molluscan remains in the various horizons of our southern Tertiaries. In these the subject matter is treated stratigraphically; in other words, the Midway stage was first taken up, then the Lignitic, and now the Claiborne is in press. Other papers dealing with special localities or horizons have also been pub- lished. In future numbers we hope to discuss all important Tertiary horizons strati- graphically. This seems the natural way for all investigation of this preliminary na- ture. Witness for example Hall’s works on the paleontology of New York as well as the paleontologic matter included in our various state survey reports. Such papers if printed in small octavo form are convenient for field use as well as laboratory study. But as years pass by and the faunas of the various horizons are better understood, and vast amounts of material collect in our museums, there comes a time when a purely biologic phase of investigation may be advantageously undertaken. Note for example the more recent works of Clarke and Ruedemann of the New York survey. This calls for a larger sized publication, admitting plates of sufficient dimensions to contain for comparison representatives of many closely allied types of life. And, the larger size page will be found not inconvenient in laboratory and museum where desks and tables are at hand; in the field, a work arranged biologically would scarcely ever be called for. Accordingly, this new work has been begun to receive such papers on invertebrate pale- ontology as are arranged systematically, papers that will be of direct assistance to stu- dents of biologic evolution. The first of these papers, unpretentious and seemingly easy of preparation, has cost the author a vast amount of study here and elsewhere to make sure that no serious omissions of specific or varietal forms have been made either in the text or plates, and that the figures and text indicate clearly the characteristic features of each form discussed. Paleontological Laboratory Cornell University -G. D. Harris October 30, 1916 Are Wy, he a es ak at nite n ein ey ae tee a A a a ¥ -. adi SOAR RAR GB aE ERS ; AA) Re aoe # = * J : he Woe p> 4 ce wh ie : i ve mit t 7 Bi 4e Re label we, . tate,’ ; aN Be raed 5 Jeattihh = U , rai 4 Baal a Dine ita - a . (jpcel Oa aA ; as Para bere ) c t ' a ] 7 ° :; oe - ‘ie : : > ’ x ett ] ay y . j ; a i ae ieee A NIC SBORE ewe AS By PRARL G. SHELDON This treatment of the Arcas* is intended to include: the synonymy, description, and distribution of the Tertiary and recent species of the genus which occur in the beds along the coast of the eastern United States; also references to the Cretaceous species, to the deep water forms which occur off the coast, and to the recent and Ter- tiary species of the Caribbean district. In measuring the specimens they were placed on crossection paper with the hinge along a horizontal line and the point of the beak on a vertical line. Measuremencs were taken from the line through the beak to the line touching the anterior point of the shell; from the line through the beak to the line touching the posterior point; from the hinge line to the highest and to the lowest points of the shell. Distances anterior to the beak and those above the hinge line were marked +, and those posterior to the beak and below the hinge line —. The diameter was measured at the widest part of the shell. Semidiam. means the diameter of a single valve. Because of the radiating sculpture and convexity of the shell, in photographing the specimens it was usually impossible to bring out the details of sculpture with equal dis- tinctness over the entire surface. In practice, the detail usually photographed best at the end away from the source of light. Ordinarily in this genus the sculpture is stronger toward the anterior and weaker toward the posterior end, therefore the specimens were usually photographed with the posterior end nearer the light in order to give a compara- tively true figure. Likewise, the angle of the teeth on the hinge varies and some cast little or no shadow. For the same reason the crenulations along the ventral margin were often lost. The muscle scars photographed indistinctly. In general, detail was lost where the light rays were perpendicular to the surface of the shell or tended to be par- allel to radial sculpture, crenulations, etc. The lighting was arranged to bring out the most important specific characters. Unless otherwise stated, the figures are natural size. Dall (Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, 1898) placed all the species under the genus A7ca and gave Barbata, Noétia, Scapharca, etc., which at various times have been given the rank of genera, the rank of subgenera and groups or sections. These di- *The major part of this paper formed a thesis presented to the faculty of the Graduate School of Cornell University in partial fulfilment of the requirements for the degree of Doctor of Philosophy. Sincere thanks are due Professor G. D, Harris for aid, suggestions and criticism. Nearly all of the Tertiary material used was collected by Professor Harris or his students. 6 PALAEONTOGRAPHICA AMERICANA 6 vitions intergrade thoroughly. Dall’s treatment of the genus has been followed. Be- sides the groups represented here Dall recognizes the following: Subgenus Barbatia. Group of A. rubrofusca Smith (Lzssarca Smith, 1876) Group of A. tortuosa L. (Trisidos Bolten, 1798,-+ 7résts Oken, 1815). Group of A. celox Benson (.Scaphula Benson, 1835, not of Swainson, 1840; Sca- phura Gray, 1847, by typographical error). Subgenus Scapharca. Group of A. senzlis Lam. (Senzlia.(Gray, 1840) Adams, 1858). Subgenus Lunarca (Gray) Adams, based on ZL. costata Gray. Possibly a malformed shell. THE TYPICAL ARKS The Arcas of the group to which 4. zoe Linné belongs have an opening in the ventral margin for the byssus; the form is often irregular; cardinal area wide and rather flat with low margins, diagonal grooves in the cardinal area disconnected instead of uniting to form continuous diamond-shaped grooves as in some of the other groups; beaks small.and pointed; hinge straight and narrow; teeth small and numerous; inner margin of the valves smooth or nearly so. Arca hatchetigbeensis Harris Plate I, Figures 1, 2, 3 Arca subprotracta Aldrich, Geol. Surv. Ala , Bull 1, p. 50, 1886, fide Harris. Arca hatchetigbeensts Harris, Bull, Am. Pal., vol. 2, no. 9, p. 47, pl. 7, figs. 10, toa, 1897. Arca hatchetigbeensis Dall, Wagner Free Inst. Sci., Trans., vol, 3, pt. 4, p. 622, 1898. “Size and general form as indicated by the figure; surface covered by well-defined but somewhat irregular, imbricate, concentric lines, crossed by raised, radiating fine costz; young shell not extremely elongate, with surface marking of equal strength everywhere; in adults the medial sinus becomes more pronounced, the radiating ribs before the sinus being stronger than those behind the same, and the shell is more or less distorted. This species differs from protracta Con.—subprotracta Heilp.—by its much less‘elongate form, broader anterior, the presence of two particularly strong costee located medially on the post-umbonal slope. By examining the type specimen of A. protracta in the Academy’s collection at Philadelphia it will be seen that it agrees somewhat more nearly with this species than would be supposed from Conrad’s figure, yet the agreement can scarcely constitute specific identity. Locality (Lignitic).—Alabama: Hatchetigbee,—/arr7s,”" 1897. A. hatchetigbeensis is closely related to the fossil form of A. umbonata, but the im- brication is finer and in A. umbonata the large ribs on the posterior slope begin about at the angle of the umbonal ridge and are subequal in size, while in A. hatchetigbeensis the largest ribs are near the center of the posterior slope; those near the cardinal mar- gin are smaller and the fine sculpture extends over the umbonal ridge to the large central ribs. AMERICAN East Coast ARCAS 7 x Dimensions. —Lon.+11,-30; alt.+3,-16; semidiam. 11 mm. Occurrence.—Lignitic Eocene of Hatchetigbee, Alabama. Type.—C. U. Museum. Arca subprotracta Heilprin Plate I, Figure 4 Byssoarca protracta Conrad, Acad. Nat. Sci. Phil., Proc. for 1847, p. 295, 1848; Journ., 2d. ser., vol. I, p. 126, pl. 13, fig. 36, 1848. Not Arca protracta Rogers, Am. Phil. Soc., Trans., vol. 5, p. 332, 1837; vol. 6, pl. 26, fig. 5, 1839. Navicula protracta Conrad, Acad. Nat. Sci. Phila., Proc. for 1854, p. 29. Arca subprotracta Heilprin, Acad. Nat. Sci. Phila., Proc. for 1881, p. 449, 1882. ‘Trapezoidal, elongated, with numerous radiating lines, some of which are double, and others alternated in size and finely crenulated; dorsal margin parallel with the base; anterior margin truncated, posterior a little concave, oblique and very acutely rounded or subangular; basal margin slightly contracted; hinge long, rectilinear, very regular and gradually increasing in width towards the extremities from the apex; cardinal area wide, depressed concave, with a few fine, impressed, angular lines. Length 1%; height 1% in. nearly. ‘A pretty species of which I found one valve only.’’—Conrad, 1848. Occurrence.—‘‘Newer Eocene [Oligocene] of Mississippi—Convad. Arca paratina Dall Plate I, Figures 5, 6, 7 Arca paratina Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 621, pl. 33, fig. 14, 1898. “Shell elongated, not very thick or high, not much distorted, but with a variable byssal gape, inequilateral, the beaks at or near the anterior fourth; moderately alate in front and behind; beaks low, pointed, not inflated, their apices slightly prosogyrate; cardinal area long, narrow, lozenge-shaped, flattish, with longitudinal striz, the site of the resilium marked on each valve by two grooves forming a small triangle, within which are traces of the inception of other grooves; sculpture chiefly of fine radial riblets over- running and somewhat imbricated by not prominent lines of growth; the radials which end on the margin of the byssal foramen are perceptibly finer than the rest, those on the posterior dorsal slope are more or less fasciculated, the ends of the fascicles dentating the posterior margin; on the dorsal anterior part the riblets increase somewhat in size, but are not fasciculated; the dorsal border in front is anterior to the rest of the margin; between the dorsal posterior extreme and the ventral posterior angle there is often an irregular, but not deep emargination; the borders of the byssal foramen are irregularly emarginate; interior smooth, the margin denticulated by the sculpture except at the foramen; hinge-line straight, minutely denticulate; the teeth in the center smaller, those towards the ends inclined outward slightly, above, and a little larger; there are about twenty three anterior and forty posterior teeth, with no marked hiatus between the series. Lon. of shell 28, alt. of hinge-line 8.5, of beaks 10, diam. at the umbonal part 1omm. It is quite possible that the shell grows to a considerably larger size. 8 PALABONTOGRAPHICA AMERICANA 8 “This species is distinguishable at once from the 4. occidentalis of the same size by its uniformly more delicate and much more numerous ribs, and by its greater length in proportion to its height. It is also usually less alate behind and of more uniform, un- distorted shape. Differences of form and proportion seem to separate it sufficiently from A. subprotracta Heilprin * * *'’—Dall, 1898. Dimensions.— Small valve, lon.+4,-11; alt.+1,-5.5; semidiam, 3 mm. Occurrence.—Oligocene of the Chipola beds on the Chipola River, and of the lower bed at Alum Bluff, Calhoun County, Florida.x—Dall. Oligocene of Bailey’s Ferry, Flor- ida, and Pliocene of the Croatan beds of North Carolina.—C. U. Museum. Area occidentalis Philippi Plate I, Figures 8, 9, 10, 11 Arca occidentalis Phil., Abbild. u. Beschr., 3, p. 14, pl. 17b, fig. ga-c, 1847. Arca zebra Swainson, Zool. Ill., No. 26, pl. 118, 1831; ea parta, Arca noe of many authors, not of Linné, Dall has separated the east American form from the Mediterranean 4. xo@ with the above synonymy, Shell oblong, inflated; hinge line as long or nearly as long as the shell; posterior end emarginate; ventral margin with an opening for the byssus; ribs numerous, smaller in the depression opposite the byssal opening, interspaces with from one to several fine riblets; along the posterior cardinal margin and the umbonal ridge radiating strips which are smooth or show only fine riblets; the depression between these smooth ridges with a few normal ribs; beaks small and pointed, little curved; cardinal area wide, flatly concave, ligament area with disconnected diagonal grooves; hinge straight, narrow, with numerous fine, vertical teeth; inner margin practically smooth; color white or yel- lowish with zigzag markings of reddish brown. Dimensions.—Lon.+18,-50; alt.+5,-25; diam. 30 mm. Occurrence.—Oligocene of the Bowden beds, Jamaica; Miocene (?) of Curacao; Pli- ocene of the Caloosahatchie marls, Florida; Pleistocene of the Florida Keys, Yucatan and most of the West Indian Islands; recent in the Antilles generally, and along the eastern coast of the United States northward to the vicinity of Cape Hatteras, North Carolina.—Dall. Recent from Florida and the West Indies.—C. U. Museum. Arca umbonata Lamarck Plate I, Figures 12, 13, 14, 15, 16, 17 Arca umbonata Vamarck, An. s. vert, vol. 6, p. 37, 1819. Arca imbricata of several authors. Arca umbonata Arango, Fauna Malacologica Cubana, p. 261, 1879. Arco umbonata Dall, Wagner Free Inst. Sci., Trans., vol, 3, pt. 4, pp. 620, 659, 1898; pt. 5, pl. 38, figs. 4, 4a, 1900 “A testa transversim oblonga, ventricosa; angulato-sinuata; decussatim substriata; umbonibus magnis, arcuatis: latere postico brevissimo. 9 AMERICAN East Coast ARCAS 9 “list. Conch= ¢; 367. £, 207. “Habite les mers de la Jamaique. Mus.no. Elle est trés-bdaillante au bord supérieur. Largeur, 50 millimétres.’’— Lamarck, 18109. Anterior and posterior are reversed in Lamarck’s description. Ribs on the center of the shell small and rather even, larger anteriorly; posterior slope with four to six larger, more widely spaced ribs; fine ribs in some of the inter- spaces, especially on the anterior part of the shell, ribs crossed by concentric raised lines which give the part of the shell anterior to the umbonal ridge an imbricated nodu- lar appearance; radial sculpture predominant on the posterior slope; umbonal ridge usually angular; cardinal area wide with diagonal grooves; teeth numerous, nearly ver- tical, smaller where the grooves cross the hinge; posterior margin nearly straight; byssal opening large; shell unevenly stained with blackish or bluish brown; epidermis long and scaly, chiefly about the margin and posterior slope. “Like all the group, this nestling species is variable in form according to its station, but I have been unable to find any characters to separate the fossil and recent shells when allowance is made for the deformations alluded to * * *.. It probably retreated to warmer waters during the Miocene invasion of Florida and did not succeed in return- ing until the end of the Pliocene, as it has not turned up in the Caloosahatchie marls. The form doubtfully identified by Professor Heilprin with A. Lzsteri is connected by a fuller series with the others.’’—Dad/. Many authors have united the Atlantic and Pacific forms under the name of A. im- bricata Bruguiére. Dall placed A. Listeri (Tryon) Heilprin, W. F. I. S. Trans., vol. 1, p. 113, 1887, and Barbatia Bonaczyi Gabb, Am. Phil. Soc., Trans., vol. 15, p. 254, 18°3, under A. umbonata. A. americana d’Orbigny, 1846, Voyage dans 1|’Amérique Mérid- ionale, Moll., p. 632; Hist. Isla Cuba, pt. 2, vol. 5, Moll, p. 342, vol. 8, pl. 28, figs 1, 2, is this species. Dimensions.—\on. +14,-31; alt.+7,-21; diam. 25 mm. Occurrence —‘‘Oligocene of the Chipola beds, Calhoun County, Florida; of the Ballast Point Silex beds, Tampa Bay, Florida; of the Alum Bluff sands at Oak Grove, Santa Rosa County, Florida. Also in the Pleistocene of the Florida Keys and the Antilles, and living from Cape Hatteras, North Carolina, south to Santa Caterina, Brazil, and throughout the Antilles.’’—Dal/. Oligocene of Bailey’s Ferry, Florida, and recent from Florida, Galveston, Texas, the West Indies, Aspinwall and Brazil—C. U. Museum. Arca wagneriana Dall Plate I, Figures 18, 19 Arca (Arcoptera) aviculeformis Heilprin, Wagner Free Inst. Sci., Trans., vol. 1, p. 98, pl. 13, figs. 32, 32a, 1887. Not Area aviculeformis Nyst, Tabl , Synopt., p. 12, 1848; Arca aviculoides Reeve, 1844, fide Dall; not A. aviculoides de Koninck, Des. An. Fos., p. 114, 1844. Arcoptera avicul@formis Dana, Man. Geol., 4th ed., p. 900, fig. 1510, 1895, Arca Wagneriana Dall, Wagner Free Inst, Sci., Trans., vol. 3, pt. 4, p. 619, 1898; pt. 5, pl. 39, figs. 6, 7, 1900. be) PALAEONTOGRAPHICA AMERICANA IO “Shell elongated, aviculaeform, rostrated anteriorly, winged posteriorly, with a prominent obtuse carination on the umbonal slope bounding the wing: rostrum decliv- ous, marked off from the body of the shell by a broad hollow; basal margin of shell sinuous, showing a median opening, and rapidly sloping upward in the direction of the rostrum; posterior border deeply emarginate. Umbones acute, very eccentric, moderately elevated, and but slightly incurved, with a gradual continuous slope to either extremity of shell; hinge-line nearly the whole length of shell, very narrow, pectinated with a crowded series of lamellar, transversely directed teeth, which exhibit a tendency to become oblique and v-shaped on the pos- terior half of the line; ligamental area broad, open, arching upward in a gentle curve, longitudinally lined, and irregularly grooved by numerous diagonal or v-shaped furrows resembling insect borings. Surface of shell ornamented with numerous radiating, wavy lines, alternating in coarseness, which become more or less obsolete on the umbonal slope, and are wholly wanting on both the beak and wing, which only show concentric lines of growth, of the radiating lines on the anterior part of the shell the series runs about as follows: coarse line, followed by two finer lines, then a slightly more prominent single line, again two finer lines, and then a coarse line, same as first, marking the coarse lines at intervals of about six or seven; interior of shell deep, cuneiform; margin entire. “Length, 5.4 inches; width across the beaks, 2.5 inches. “Caloosahatchie, in the banks below Fort Thompson.’’—//e7/prin, 1887. “This fine species is quite variable in the development of the extended wings which suggested Professor Heilprin’s name. In many specimens the posterior wing does not exceed that usualin A. occidentalis, while in others it may extend an inch beyond the rest of the shell. The anterior wing is less prominent and not a little more constant, but is frequently paralleled by fossil and even by recent specimens of A. occidentalis Phil. So far as yet known this species is confined to the Floridan Pliocene. The character of the cardinal area is similar to that of A. noe.’’—Dall. The anterior as well as posterior teeth may be v-shaped. The ribs are finer than in A. occidentalis. Dimensions.—(Small valve), lon.+-16,-29; alt.+-3,-13; semidiam. 8 mm. Occurrence.—Pliocene marls of the Caloosahatchie, Shell Creek, and Myakka River. —Dall. Pliocene of Shell Creek, Florida.—C. U. Museum. Arca aquila Heilprin Plate II, Figures 1, 2 Arca aquila Heilprin, Wagner Free Inst. Sci., Trans., vol. 1, p. 97, pl. 12, fig. 31. 1887. Arca aquila Dall, Wagner Free Inst. Sci., Trans , vol. 3, pt, 4, p. 621, pl. 31, fig. 12, 1898. “Shell (known only by its left valve) elongated, rectangular, winged, profoundly sulcated on the posterior slope; anterior border vertical, straight; basal line slightly sinuous beyond the middle; hinge-line straight, of nearly equal length with the base; teeth very numerous, gradually increasing in size toward either end, where they are II AMERICAN East Coast ARCAS II markedly oblique: hinge-area broad, obscurely furrowed in longitudinal lines; beak moderately elevated, incurved, the apex directed backward; surface of the shell radiate- ly ribbed, the ribs sinuous, beaded—especially on the anterior portion of the shell, where they are separated by an intermediate fine line—becoming obsolete in the poster- ior sulcus and on the wing where they are represented by two pairs of lines; lines of growth prominent towards the base and on the wing; basal margin crenulated. “Length 1.25 inches; height, from base to hinge-line, .5 inch.’ “This winged ark is at once distinguished from A. aviculeformis * * * by the ab- sence of the anterior rostrum and its rectangular form. The last character, in addition to differences in the ornamentation, also serves to distinguish it from the Miocene A7ca incile, which resembles it somewhat in the pterination of the posterior slope—.’’ Hedprin, 1887. “This very neat species appears to be somewhat rare, and has only been found in the original locality as yet.’’—Dadl. Occurrence.—‘*Pliocene marls of the Caloosahatchie River, Florida.’’—Dad/. Arca bowdeniana Dall; Plate II, Figure 3; (Wagner Free Inst. Sci., Trans., vol. 3, p. 622, pl. 33, fig. 12, 1898) from the Oligocene of the Bowden beds, Jamaica, and Phio- cene of Limon, Costa Rica, is a small species with very anterior beaks and sculpture like that of A. uwmbonata and the diameter is greatest posteriorly. Subgenus Barnatia (Gray) Adams Barbatia Gray, Synops. Brit. Mus., 1840, p. (?); ibid , 1844, p. 81. Type Arca barbata L,.,H and A. Adams, Gen. Rec. Moll., ii., p. 534, 1858. “The type form of this group is tolerably regular and seldom deformed, like the typical Arks, from the anfractuosities of its station; the reticulated sculpture shows few irregularities; the cardinal area is narrow with numerous grooves for the resilium, which forms a series of elongated concentric lozenges on the area; the shell is not conspicuously truncate or keeled; the teeth are small and vertical in the middle of the series and toward the end diverge distally and become larger and more distant. In some species these distal teeth are often broken up, like those of Cucnllea, but this feature is not con- stant in the species. Several groups or sections are recognizable, though they range into one another through their peripheral species. Such are the following: “Group of 4. barbataL. (Barbatias,s.). This includes A. (B.) mississippiensts Conrad from the Vicksburgian Oligocene. “Group of 4. candida Gmelin (Calloarca Gray, 1857,+/Plagiarca Conrad, 1875). This includes A. cuculloides Conrad (+A. lima Conrad, 1847 not of Reeve, 1844,—4. Conradi Desh,) from the Jacksonian; 4. marylandica Conrad and A. arcula Heilprin, Upper Oligocene and Older Miocene; and several other species. Litharca (lithodomus) Gray, 1840, is probably based on a specimen of 4. candida, which had grown in the burrow of a Lithodomus. Upper Cretaceous to recent. 12 PALAKONTOGRAPHICA AMERICANA 12 Group of A. propatula Conrad (Granoarca Conrad; 1862)—=A. hians Tuomey and Holmes, 1855, not of Brown, 1842; nor of Reeve (?—A. frotracta Rogers, not of Conrad, 1847). Miocene. Group of A. centenaria Say (Striarca Conrad, 1862). Miocene. Group of A. donaciformis Reeve (Acar Gray, 1847,-+-Daphoderma Moerch, 1853, +Fossularca Cossmann, 1887. Eocene to recent. “In Striarca the lozenge occupied by the ligament and its transverse grooves for the resilium cover the entire cardinal area; in typical Acar the lozenge is obliquely di- rected backward, leaving the anterior part of the area bare; in Fossularca the lozenge is small, very short, and directly between the beaks, leaving a bare space before and be- hind it. A. celata Conrad (A. Adams Shuttleworth) is a typical Fossularca. “Group of 4. Acterodonta Dash. (Les Cucullaires Desh., 1860: Cucullarta Conrad, 1869,-+Memodon Conrad, 1869). Cretaceous (Ripley) to recent. “Tn the Barbatias as well as in G/ycymeris (Pectunculus auct.) the growth of the shell often results in a greater or less absorption of the middle part of the series of teeth; the distal teeth are always more or less oblique, especially those behind the beaks. In Cz- cullaria the latter are about, if not quite, parallel with the hinge-line. Consequently, it may follow that in the process of growth the same individual may at an early stage have a series of vertical median denticles, and at a later stage may present a hiatus des- titute of teeth between the anterior and posterior parts of the series. Judging from the species I have been able to examine, the entire narrow cardinal area is originally cov- ered by the ligament, but the grooves containing the resilium extend very obliquely backward from the beaks, asin typical Azar. Notwithstanding the resemblance of the hingein these Tertiary and recent species to that of the Paleozoic and early Mezozoic Parallelodon, 1am of the opinion that the relations of the former are really closer with the true Arks, and that the similarities will prove to be analogical rather than homo- logous. The recent abyssal species I have formerly referred to Macrodon, should prob- ably be grouped under Cucullaria.’’—Dall, 1898. Arca barbata Linné Plate II, Figures 4, 5, 6, 7 Arca barbota Linné, Syst. Nat., p. 693, 1758. “Pectunculus & fusco rufescens, admodum dense striatus,” Lister, Hist. Conch., tab. 231, fig. 65, 1170. Arca barbata Gmelin, Syst. Nat., vol. 6, p. 3306, 1792. Arca borbota Reeve, Conch. Icon., pl. 13. Avca no. 83, 1844. Barbatia barbata H. and A. Adams, Gen. Rec, Moll., vol. 2. p. 534, pl. 124, figs, 4, 4a, 4b, 1858. Arca barbata Arango, Fauna Malacologica Cubana, p. 263, 1879. Arca (Barbatia) barbata Dall, U. S. Nat. Mus., Bull. 37, p. 40, 1889. Barbatia barbata Dall, Wagner Free [nst., Sci, Trans., vol. 3, pt. 4, pp. 614, 615, 659, 1898. ‘‘A. testa oblonga striata apiicbus barbata, natibus incurvis approximatus, margine inte- gerrimo clauso. Mus: Lessin, wx6s 20072 1, Bonan. recr. 2. t. 79. 13 AMERICAN East Coast ARCAS 13 Gualt, test. 91. f. F. Argenv. conch. t, 25. f. M. flabitat in M. Mediterraneo. “Testa apice rotundata, integra, strie ex punctis callosis concatenatis: alternis strtis majort- bus. Barba ex strits versus apicem imprimis tenuiorem rigens.’’—Linné, 1758. This species is irregularly colored with light and dark brown, the ribs are granulated, numerous and fine with slightly larger ribs at intervals on the middle of the valve; epi- dermis bristly; teeth fine at the center of the hinge, long and oblique distally; ligament area with several v-shaped grooves; inner margin smooth; byssal opening usually small. Dimensions.—Lon.+17,-32; alt.+5,-22; diam. 20 mm. Occurrence.—Recent from North Carolina to Barbados.—Dal/. Recent from the Mediterranean, Florida and the West Indies.—C. U. Museum. This is a common re- cent and fossil European species. Arca cuculloides Conrad Plate II, Figures 8, 9, 10, 11, 12 Arca cuculloides Conrad, Fos. Tert. Form., p. 37, 1833. Byssoarca cuculloides Conrad, Am. Journ. Sci., 2d. ser., vol. 1, p. 219, 1846. Byssoarca lima Conrad, Acad. Nat. Sci. Phila., Proc. for 1847, p. 295; Journ., 2d. ser., vol. I, p. 125, pl. 13, fig. 23, 1848=A. Conradi Deshayes. Not Arca lima Reeve, Conch, Icon., Avca no. tor, 1844. Navicula cuculloides et lima Conrad, Acad. Nat. Sci. Phila., Proc. for 1854, p. 29. Cucullearca lima et cuculloides Conrad, Am. Journ. Conch., vol. 1, p. 11, 1865. Barbatia (Calloarca) cuculloides Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, pp. 615, 624, 1898. “Shell compressed, thick, inequivalve, reticulated; with a broad subcentral sinus, passing from the beak to the basal margin: posterior side elongated, strongly ribbed, and carinated; anterior side with numerous strize; anterior end truncated. Length 214 in- ches. Breadth 1% inches. “The hinge of this shell approaches cuculleea, in the interval between the beaks, hav- ing arcuated grooves under the beak; line of series of hinge teeth widely interrupted, and transverse at the extremities. “Locality. Claiborne, Alab. “Cab. Acad. N. S.’—Conrad, 1833. Ribs smallest near the middle of the valve, becoming wider and smoother toward the umbonal ridge and larger and more widely spaced anteriorly; posterior slope with small, smooth ribs, this region separated from the rest of the shell by a sharp radial ridge which is often serrate; ribs anterior to the umbonal ridge mostly nodular and with finer ribs in some of the interspaces; cardinal area longer behind with numerous regular grooves; teeth continuous in the young, those in the center very small, distal teeth long and oblique, usually irregular in old specimens; outline variable, shell higher posteriorly. The ribbing varies on different shells, but the species is characterized by the sharp rib down the umbonal ridge and the ribs usually are quite different on different parts of the shell. 14 PALAEONTOGRAPHICA AMERICANA 14 The variety figured and described by Professor Harris (Bull. Am. Pal., vol. 2, no. 9, p. 47, pl. 8, figs. 1, ra, 1897), has a more pointed posterior basal angle and rougher pos- terior ribs than the type. It is from the Sabine Eocene of Gregg’ s Landing, Alabama. Navicula aspersa Conrad, Wailes, Agr. and Geol. Mississippi, p. 289, pl. 14, fig. 5, 1854; Navicula aspera Conrad, Acad. Nat. Sci. Phila., Proc. for 1855, p. 258, 1855; not d7ca aspera Phil., Moll. Sicil., 1836 (Ade Dall) has been listed in synonymies as the young of A. cuculloides, but the specimen in the Philadelphia Academy is Acar reticulata. Dimensions. —Lon.+18,—40; alt.+7,-39 ; semidiam. 19 mm. Occurrence.—Upper Eocene (Jacksonian) near Claiborne, Alabama; Jackson, Missis- sippi; Cleveland County, Arkansas; and in the Lower Oligocene at Vicksburg, Missis- sippi—Dall. Sabine Eocene of Gregg’s Landing, Alabama and Pendleton, Texas, and Jackson Eocene of Jackson, Mississippi, of Montgomery, Grandview Bluff, Gibson's Landing and Bunker Hill Landing, Louisiana and of Texas,—C. U. Museum. Arca mississippiensis Conrad Plate III, Figures 1, 2, 3, 4 Byssoarca mississippiensis Conrad, Acad. Nat. Sci., Phila., Proc. for 1847, p. 295; Journ., 2d. ser., vol. I, p. 125, pl 13, fig. 32, 1848. Not Arca mississippiensis Conrad, Acad. Nat. Sci. Phila., Journ., 2d. ser., vol. 1, p. 125, pl. 13, figs. 11, 15, 1848. Navicula mississippiensis Conrad, Acad. Nat. Sci. Phila., Proc. for 1854, p. 29. Cucullearca mississippiensis Conrad, Am. Journ. Conch., vol. 1, p. 11, 1865. Barbatia mississippiensis Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 625, 1898. “Trapezoidal, with numerous closely arranged radiating lines, crenulated by fine concentric lines, the crenulation most distinct anteriorly, where the radii are largest; an- terior end truncated or a little convex, direct: posterior margin obliquely truncated above; basal margin widely and profoundly arched; hinge line long, linear, minutely crenulated, expanded towards the extremities, and with prominent teeth; cardinal area with fine, very closely-arranged lines, angulated under the apex. Length 1 6-10. “Differs from the preceding [2. ma] in having a longer hinge, finer radii, etc., and is a much smaller species and more abundant.’’—Conrad, 1848. This species is much like 4. marylandica. It is separated from A. cuculloides by its even ribbing and lack of the sharp umbonal ridge which characterizes that species. Dimensions.—(Small valve), lon.+9,-20; alt,+-2.5,-16; semidiam. 6 mm. Occurrence.—Vicksburg Oligocene of Vicksburg, Mississippi.—C. U. Museum. Arca marylandica Conrad Plate III, Figures 5, 6, 7 Byssoarca marylandica Conrad, Fos. Med. Tert., p. 54, pl. 29, fig. 1, 1840. Navicula marylandica Conrad, Acad. Nat. Sci. Phila., Proc. for 1854, p. 29. Barbatia ( Byssoarca) marylandica Conrad, Acad. Nat. Sci. Phila., Proc. for 1862, p. 580, 1863. Arca marylandica Heilprin, Acad. Nat. Sci. Phila., Proc. for 1880, p. 21. Barbatia ( Calloarca) marylandica Dall, Wagner Free Inst. Sci., Trans., vol. 3; pt. 4, p. 623, 1898. Arca (Barbatia) marylandica Glenn, Maryland Geol. Survy., Miocene, p. 392, pl. 106, fig. 7, 1904. 15 AMERICAN East Coast ARCAS 15 “Shell oblong, compressed, thin, with very numerous radiating granulated striae; beaks not prominent; base much contracted or emarginate anterior to the middle; posterior side dilated, the superior margin very oblique and emarginate; extremity angulated, and situated nearer to the line of the hinge than to that of the base; cardinal teeth minute, except towards the extremities of the cardinal line, where they are comparatively very large and oblique; inner margin entire. “Locality. Cliffs of Calvert, Md. * * *.’’—Conrad, 1840. Ribs not varying conspicuously over the shell, often alternating with finer ribs an- teriorly, smoother and usually double posteriorly; posterior part of the shell two-angled or broadly rounded; cardinal area with numerous v-shaped grooves; form of shell often irregular. This species lacks the sharp umbonal ridge of A. cuculloides. Byssoarca marilandica Lea, Acad. Nat. Sci. Phila., Proc. for 1848, p. 97, and Arca marylandicus Heilprin, Acad. Nat. Sci. Phila., Proc. for 1881, p. 451, are misprints for this species. Dimensions.—Lon. +17,-36; alt.+-6,-30; semidiam. 14 mm. Occurrence.—Oligocene of the Ballast Point silex beds, Tampa Bay, the lower (Chip- ola) bed at Alum Bluff, the Chipola marl of the Chipola River, Florida; older Miocene of Jericho, Cumberland County, New Jersey; Middle Miocene of Plum Point, Calvert Cliffs, and Centreville, Maryland. Possibly also in the Jacksonian.—Dal/. Calvert Mi- ocene of three miles west of Centreville, Plum Point, Centreville, Maryland.—Glenn. Oligocene of Bailey’s Ferry, Florida.—C. U. Museum. Arca arcula Heilprin Plate III, Figures 8, 9 Arca arcula Heilprin, Wagner Free Inst. Sci., Trans., vol. 1, p. 118. pl. 16, fig. 65, 1887. Barbatia ( Calloarca) arcula Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 624, pl. 33, fig. 4, 1898. “Shell moderately elongated, sharply angulated on the posterior slope, the dorsal and ventral borders nearly straight and parallel with one another; dorsal (hinge) line not much more than half the length of shell; anterior border projecting forward basally; posterior border acutely angulated with the base; beaks anterior, not very prominent, nor very widely separated; ligamental area narrow; teeth almost obsolete in the middle of the hinge-line, becoming oblique toward either extremity; interior of shell deep; ex- ternal surface closely ribbed, the ribs strongly imbricated by the rugose lines of growth; ribs most prominent on the posterior slope, where they are echinated. “Length, 1.7 inch; height to top of umbo, 1 inch.’’—/H/ez/prin, 1887. “Shell subovate, thin, inflated, the beaks low and prosogyrous; the cardinal area narrow and very closely and minutely furrowed longitudinally, the furrows showing a slight angle behind the beaks; sculpture of close set, fine radial ribs, rather regularly imbricated at successive lines of growth; on the posterior dorsal slope are six or eight nodulous larger ribs; the beaks are situated a little behind the anterior third; byssal foramen narrow, very anterior; hinge with a few large v-shaped teeth at the ends, the 16 PALAKONTOGRAPHICA AMERICANA 16 middle teeth vertical, small, or even obsolete mesially; margins of the valve slightly or not at all crenulated by the sculpture. Length of shell 47, of hinge-line 30, height 31, diameter 26 mm. “This species is very evenly and regularly fluted at the imbrications, differing in that respect from any of the other species mentioned here. It is notable also for its in- flated and thin valves and the bluntly truncate posterior end, though the latter may be abnormal.—Dall.”’ Occurrence.—Oligocene of the Ballast Point silex beds, Tampa Bay, Florida.—Dal. Arca phalacra Dall Plate III, Figure ro Barbatia (Calloarca) phalacra Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 626, pl. 33, fig. 3, 1898. “Shell thin, moderately convex, equivalve, inequilateral ; the prosogyrate beaks within the anterior fourth low and somewhat compressed; sculpture of very numerous fine, even, mostly dichotomous riblets without noduies or reticulation over the whole shell, crossed only by feeble incremental lines; cardinal area very narrow, with a few longitudinal grooves; hinge-teeth small, short, and vertical mesially without any gap in the series, distally longer, larger, and more oblique; hinge-line 0.6 of the whole length; internal margin of the valves smooth, byssal gape inconspicuous. Lon. 23.5, alt. 11, diam., 9 mm. “This isa very modest and neat little species which does not seem identifiable with any of the others. It is, perhaps, nearest to B. mississippiensis Conrad, but is smaller, less flattened, and more regular.’’—Dal/, 1898. Occurrence.—Oligocene of the Chipola marls, Chipola River, and of the Oak Grove . sands, Florida.—Dal/. Arca candida Gmelin Plate III, Figures 11, 12 Arca candida Helblingi, Chemnitz, 7, p. 195, pl. 55, fig. 542. Arca candida Gmelin, Syst. Nat., 6, p. 3311, 1792. Arca Helblingii Bruguiere, Encye. Meth., p 195, 1797. Arca jamaicensis Gmelin, Syst. Nat., 6, p. 3312, 1792. Barbatia (Calloarca). candida Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 626, 1898, “A. testa pellucida rhomboidali anterius producta posterius truncata decussatim striata : natibus remotis, margine posterius hiante ; hiatu ovato ciliato. Chemn. Conch. 7. t. 55 £. 542. B) Chemn. Conch. 7. t. 55. f. 544. Habitat in Oceano americano e/ ad Africee littus occidentale, /esta alba, quast granu- lata, epidermide villosa ex atro subfusca obducta,’’—Gmelin, 1792. The synonymy is taken from Dall, who says, ‘‘There are some difficulties in the 17 AMERICAN East Coast ARCAS 17 nomenclature of this species which I have not the literature to straighten out. As far as I am now able to ascertain, the first name applied to this shell was candzda, and the first binomial Latin name was that of Gmelin. It is a well known West Indian species conspicuous for its large size, white shell, and compressed, flattish valves. It is quite possible that some of the early authors named this wide-spread species more than once, and in this connection the A. ovata and complanata should be examined.’’ Recent and fossil shells from the Caribbean district reported as 4. velata Sowerby are probably this species. “Shell thin to solid, rather compressed, subtrapezoidal, gaping at the anterior base; anterior end generally truncate; posterior end pointed and obliquely truncate above; beaks high, separated by a moderately wide area; surface sculptured with fine to rather strong double or single, large or small ribs which are heavier on the posterior slope. These are crossed by rude, irregular growth lines and ridges, causing the surface to ap- pear somewhat cancellated and beaded; epidermis heavy, shaggy; teeth feebly devel- oped. Color white. “Length, 60; height, 35; diameter, 28 mm,’’—Dal/ and Simpson, (Mollusca of Porto Rico, Bull. U. S. Fish Comm., vol. 20, for 1900, pt. 1, p. 460, 1901). Occurrence.—Oligocene of the Bowden beds, Jamaica, of the Chipola beds at Alum Bluff and on the Chipola River, Florida; Pliocene of Trinidad; Pleistocene of the An- tilles generally, and recent from Cape Hatteras, North Carolina, to Brazil at Santa Cat- erina, and possibly the African coast.—Dall. Recent from Santo Domingo.—C. U. Museum. Arca caloosahaichiensis (new name) Plate III, Figure 13 Barbatia ( Calloarca) trregularis Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 623, pl. 33, fig. 5, 1898. Not Arca irregularis Deshayes, Des. Coq. Fos., vol. 1, p. 208, pl. 32, figs. 9, Io, 1830. Not Arca irregularis d’Orbigny, Pal. Frang., Terr. Crét., vol. 3, p. 240, pl. 326, figs. 4, 5, 1844. “Shell thin, elongate, irregularly distorted; beaks prosogyrate; at the anterior third rather low and compressed; cardinal area long, rather narrow, with very numerous (twelve) concentric grooves; surface irregular, sculptured with numerous fine radiating, somewhat imbricated ribs, of which those in front of the beaks and on the posterior dor- sal slope tend to be larger and more elevated; there isa tendency to alternate or pair among the ribs in some specimens; the imbrications or nodules on the ribs are somewhat regularly spaced and correspond to elevated concentric lines in harmony with the lines of growth; the posterior dorsal slope is bounded by rounded ridges radiating from the beaks; the posterior cardinal margin is elevated and angular with more or less of a de- pression between it and the radial ridge on each side; the byssal foramen is wide and ir- regular; the hinge-line is long and straight; the teeth, vertical and very small medially, are sometimes obsolete in the middle of the hinge; distally they become rather distant and quite oblique, as well as larger; the internal margin, though irregular, is not fluted. Lon. of adult 51, alt. 25, diameter 20 mm. 18 PALAEONTOGRAPHICA AMERICANA 18 “This species is distinguished from &. marylandica by its smaller altitude, its coarser and more prominent sculpture, and more irregular hinge; the beaks are also more anterior.’’—Dall, 1898. Occurrence.—Oligocene of the silex beds at Ballast Point, Tampa Bay (fragment)? Pliocene marls of Shell Creek, Alligator Creek, and the Caloosahatchie.—Da//. Arca nodulosa Miller Plate III, Figures 14, 15 Arca nodulosa Miller, Zoologize Danicze Prodromus, p. 247, 1776. Arca nodulosa Gmelin, Syst. Nat., vol. 6, p. 3309, 1792. Arca nodulosa Broegger, Norges Geologiske Undersogelse, No. 31, pl. 15, figs. 13a, 13b, Igor. “Arca testa oblonga nodulis striata, natibus incurvis remotis, margine integerrimo clauso. Mill. zool. dan. prodr. 2984. Habitat in omni mari europeo, fabe equine magnt- tudine, natibus approximatis.’’—Gmelin, 1792. Dall (U. S. Nat. Mus,, Bull. 37, p. 42, 1889; Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 659, 1898), places this species in Calloarca and lists it from the Florida Keys. Thiele (Zool. Jahrb., Jena, Suppl. 11, pt. 2, p. 127, 1910), lists it from St. Thomas. It occurs as a fossil in Europe. Arca propatula Conrad Plate IV, Figure 1 Arca propatula Conrad, Acad. Nat. Sci. Phila., Proc. for 1843, p. 323; Fos. Med. Tert., p. 61, pl. 32, fig. 1, 1845. Arca hians Tuomey and Holmes, Pleioc. Fos. S. Car., p. 34, pl. 14, figs. 4, 5, 1855. Not of Bronn, 1842 (fide Dall), or Reeve, Conch. Icon., Arca no. 62, 1844. Arca hians Whitfield and Hovey, Am. Mus. Nat. Hist., Bull., vol. 11, pt. 4, pp. 444-447, 1901. Barbatia (Granoarca) propatula Conrad, Acad. Nat. Sci. Phila., Proc. for 1862, pp. 290, 580, 1863. Arca (Granorca) propatula Tryon, Struct. and Syst. Conch., vol. 3, p. 254, pl. 129, fig. 5, 1884. Barbatia (Granoarca) propatula Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 627, 1898; pt. 6, p. 1601, 1903. “Rhomboidal, thick and ponderous; posterior side produced; sides flattened, slight- ly concave toward the base; umbonal slope rounded, rather elevated; ribs about 32, square, not profoundly prominent, about equal in width to the interstices, which have transverse imbricated lines; ribs largest about the umbonal slope, very distinct on the posterior slope, which is concave towards the hinge-line; posterior margin oblique, con- cave extremity widely rounded; summit of umbo moderately elevated, slightly retuse; cardinal area wide, with diverging grooves; series of teeth slightly sinuous anteriorly; teeth numerous; at the posterior extremity, the series suddenly becomes dilated, and the teeth interrupted or tuberulcar; inner margin crenate; crenze profound and remote posteriorly. Length, four inches; height rather more than one and one-third inches. “Tocality. James River, below City Point. Petersburg, Mr. Tuomey; Ware River, Gloucester County, Virginia, Mr. Ruffin. “Perhaps this may prove to be an old specimen of A. avata, Say.’’—Conrad, 1843. 19 AMERICAN East Coast ARCAS 19 Tuomey’s shell was proportionately longer than Conrad’s. Occurrence.—Miocene of Virginia, on the James River below City Point, Petersburg, and on the Ware River, Gloucester County; Darlington, South Carolina; Sumter Dis- trict, South Carolina.—Dadll. Arca virginiae Wagner Plate IV, Figures 2, 3, 4 Arca virginie W. Wagner, Trans. Wagner Inst., v., pl. 1, fig. 3 (ide Dall). Arca virginie Bronn, Index Pal. Nomencl., p. 99, 1848; Syst., p. 281, 1849. Barbatia (Granoarca) virginie Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 627, pl. 32, fig. 23, 1898. Arca (Barbatia) virginie Glenn, Maryland Geol. Surv., Miocene, p. 392, pl. 106, fig. 8, 1904. “Arca virginié is a large, solid, elongated shell, equivalve but very inequilateral, the beaks being situated near the anterior fifth of the length, low and prosogyrate, dis- tant, and separated by a wide cardinal area with numerous (nine) slightly angular longi- tudinal concentric grooves; sculpture of about twenty-five strong radial ribs, smaller on the posterior dorsal area, somewhat flattened, and on the posterior part with a shallow, wide mesial furrow; hinge-line .65 as long asthe shell; teeth vertical, in two series, be- ginning mesially very small, distally larger, and with a tendency to break up or become irregular; muscular impressions deep; margin fluted in harmony with the ends of the ribs. Lon. 83, alt. 52, diam. 42 mm. ‘*This shell is about midway in its characters between Barbatia (Granoarca), Ana- dara, and Scapharca, illustrating very well the manner in which the subordinate groups of the genus Avca intergrade * * *.’’—Dall. Occurrence.—Miocene of Virginia, (Nansemond River?)—VDall. St. Mary’s Miocene of St. Mary’s River, Maryland, (imperfect, probably this species).—G/ennx. Miocene of Claremont Wharf, James River, Virginia —C. U. Museum. Arca centenaria Say Plate IV, Figures 5, 6, 7 Arca centenaria Say, Acad. Nat. Sci. Phila., Journ., 1st. ser., vol. 4, p. 138, pl. 10, fig. 2, 1824. Striarca ( Arca centenaria Conrad, Acad. Nat. Sci. Phila., Proc. for 1862, pp. 290, 580, 1863. Barbatia (Striarca) centenaria Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, pp. 615, 628, 1898; pt. 6, p. 1601, 1903. Arca ( Barbatia) centenavia Glenn, Maryland Geol. Snrv., Miocene, p. 391, pl. 106, figs. 5, 6, 1904. “Shell transversely oval, subrhomboidal, obtusely contracted at the base with nu- merous alternate longitudinal striz. ‘ck %* ** Strize from one hundred to one hundred and eighty and more in number; disappearing on the hinge margin; with hardly obvious transverse minute wrinkles, and larger, remote, irregular ones of increment: beaks but little prominent, not remote: base widely but not deeply contracted, nearly parallel with the hinge margin: anterior and posterior margins obtusely rounded: series of teeth rectilinear, uninterrupted, decurved at the tips; space between the beaks with numerous grooves proceeding from the teeth: 20 PALEAONTOGRAPHICA AMERICANA 20 inner margin not very distinctly crenated: muscular impressions elevated, and forming a broad line each side, from the cavity of the beak to the margin. “Length nine-tenths of an inch, breadth nearly one inch and a half.’’—Say, 1824. Say used the term length for height and breadth for length. This species does not closely resemble any other American Avca. The beaks are elevated and little curved; the ligament area is transversely striated, each groove cor- responding with a groove in the ligament; the teeth are usually partly dissolved so that they are hollow, as in the fossil Adamsz; the upper edge of the line of teeth is straight, but the lower edge is evenly arcuate, so that the teeth are very short at the center and increase in length toward the ends of the hinge, where they make an angle of 45 de- grees with the hinge-line; the extreme distal teeth are shorter and nearly horizontal; the inner margin is nearly smooth except in the young. Dimensions.—Lon.+15,-25; alt.t5,-24; semidiam. 12 mm. Occurrence.—Older Miocene of Jericho, Cumberland County, New Jersey, and in the Virginia Miocene at Coggin’s Point, Petersburg, Grove Wharf, on the James River, and the Miocene beds of the York River.—Dad/. Choptank Miocene of Jones Wharf; Cal- vert Miocene of Church Hill, Fairhaven, Maryland.—Glenn. Miocene of Evergreen, James River, Yorktown, Kingsmill, Bellefield and Grove Wharf, Virginia.— C. U. Museum. Arca reticulata Gmelin Plate IV, Figures 8, 9, 10, 12, 12 Arca reticulata Gmelin, Syst. Nat., 6, p. 3311, 1792. Arca reticulata Chemnitz, Conch. Cab., 7, p. 193, pl. 54, fig. 540. Arca squamosa. domingensis et clathrata lam., An. s. Vert., vol. 6, pp. 45, 40, and 46, 1819. Arca gradata Brod, and Sby., Zool. Journ., vol. 4, p. 365, 1829. Arca divaricata Sby., P. Z. S., 1833, p. 18; Reeve, Conch. Icon., Arca, pl. 16, fig. 108, 1844. Barbatia (Acar) reticulata Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 629, 1898. “A testa subrhomboidea decussatim striata alba: natibus approximatis, vulva cor- data. List. Conch. t. 233. £. 67. Martini Besch, Berl. Naturf. 3. t. 6. f. 9. Chemn. Conch. 7. t. 54. £. 540. Habitat - - - arcae Noae affinis, utrum hujus, an sequentis familiae?’’—Gmelin, 1792. The synonymy is taken from Dall. This includes forms of varietal value. Speci- mens in the Newcomb collection from Panama and Trinidad are radiately and concen- trically ridged, the concentric ridges the stronger on the middle of the shell, giving rise to the name gradata, the diverging, radiating ridges are about as strong as or stronger than the concentric ridges on the posterior slope, but the sculpture is not conspicuously different on different parts of the shell. Only the posterior part of the cardinal area is covered by the ligament; the inner margin is finely crenulated. A specimen from Cuba is very similar to one labelled Acar donaciformis from the Mediterranean. These are smaller and thicker and the crenulations on the posterior inner margin are not so closely 21 AMERICAN East Coast ARCAS 21 connected with the external sculpture, but form long, even ridges on the thick margin. Specimens labelled from Paumotus and from the Mediterranean which are evidently A. divaricata are thin and the sculpture of the posterior part is conspicuously different from that of the rest of the shell, the ribs there are fewer than in the other forms, more conspicuously diverging and are much stronger than the concentric sculpture. The pos- terior ribs rise along the umbonal ridge. The crenulations of the posterior margin are larger to correspond with the larger posterior ribs and a secondary set of fine wrinkles overruns the main crenulations. Acar reticulata is characterized by its small, nearly white, well-sculptured shell, con- centric ridges and posterior ribs rising along the umbonal ridge. The teeth are grooved at the sides and many of them are v-shaped. The name clathyvata was used by Defrance (1816), M’Coy and Reeve, sgwamosa by de Koninck (1842), and reticulata by M’Coy (1844). Navicula aspersa Conrad is this species, not the young of A. cucullotdes. Dimenstons.—Large shell, lon.+-10,-17.5; alt.+3,-13; diam. 15 mm. Oceurrence—Eocene of the Jacksonian at Moody’s Branch, Jackson, Mississippi; Oligocene of the Bowden beds, Jamaica; Matura, Trinidad; of the Tampa silex beds at Ballast Point, Florida, and on the Chipola River, Pliocene of Limon, Costa Rica, and of the Caloosahatchie marls; Pleistocene of the Antilles generally; and recent from Cape Hatteras to Barbados and the Gulf of Campeachy.—Da//. Recent from Trinidad, Cuba, Panama, Paumotus and the Mediterranean.—C. U. Museum. Arca millifila Dall Plate IV, Figures 13, 14 Arca (Acar) millifila Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 6, pl. 56, figs. 21, 24, 1903. “Pliocene marl of Shell Creek, Florida; the ligament is typical of Acar, the radial threads are minutely granular, especially on the posterior dorsal slope; the shell is thin and the scars obscure.’’—Dal/, 1903. Arca Harrisi (new name) Plate IV, Figure r5 Arca inornata Meyer, Geol. Surv. Ala , Bull 1, p. 79, pl. 1, fig. 24, 1886. Arca inornala deGregorio, Faune Eocénique de 1’ Alabama, p. 197, pl. 24, fig. 29, 1890. Arca (Fossularca?) inornata Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 658, 1898. Not Arca ( Cucullaa) inornata Meek and Hayden, Acad. Nat. Sci. Phila., Proc. for 1858, p. 51, 1858. “Trapezoidal; anterior side truncated, flat; beak small; ligament area very low; teeth smallest toward the middle; covered with indistinct concentric lines; margin entire. “Resembles Arca levigata, Caillat, from the Paris basin, but is less oblong.’’ 1886. From the descriptions this species appears to be nearest /ossularca. The name zzor- nata is preoccupied by Meek and Hayden. Their species, from the Black Hills, has been placed in Grammatodon. Meyer’s species is renamed in honor of Professor G. D. Harris for his work on the Eocene. Occurrence.—Eocene of Claiborne, Alabama.—/VZeyer. —Meyer, 22 PALAEONTOGRAPHICA AMERICANA 22 Arca Adamsi (Shuttleworth) Smith Plate IV, Figures 16, 17, 18; Plate V, Figure 1 Arca celata Conrad, Fos. Med. Tert., p. 61, pl. 32, fig. 2, 1845. Not Arca ce@lata Reeve, Conch. Icon., Avca no. 110, 1844. Barbatia (Arca) celata Conrad, Acad. Nat. Sci. Phila., Proc. for 1862, p. 580, 1863. Arca lactea of various authors, not of Linné. Arca (Acar) Adamsii Shuttleworth, MS.?, Smith, Lin. Soc., Zool., Journ., vol. 20, p. 499, pl. 30, figs. 6, 6a, 1890. Arca Adamsi Dall, Bull. Mus. Comp. Zool. Harvard, vol. 12, p. 243, 1886. Barbatia (Fossularca) Adamsi Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 629, 1898. “Trapezoidal, disk widely and not profoundly contracted; ribs numerous, alternated towards the base, tuberculated, aculeated anteriorly and posteriorly; posterior slope de- pressed; umbo acutely angulated behind; basal margin slightly arched; posterior margin obliquely truncated; beaks approximate. “Loc. Wilmington, N. C., Mr. Hodge.’’—Conrad, 1845. ‘‘This species is well distinguished from the similar looking A. /actea of Europe by the fact that its radial riblets are formed by rows of trailing blisters or hollow flutings, which are very friable and often entirely worn off, leaving the shell practically smooth. Though the shell has long been labelled with Shuttleworth’s name in collections, the first published description I have met with is that of Mr. E. A. Smith, * * * Conrad’s spe- cific name is preoccupied. The fossils agree exactly with the living specimens, except that those from the Oligocene are usually somewhat smaller than the full-grown recent shells.’’—Dall. Ligament occupying only a small, diamond shaped area between the beaks; line of teeth interrupted opposite the ligament. Dall, (Bull. Mus. Comp. Zool. Harvard, vol. 12, p, 243, 1886; U. S. Nat. Mus., Proc., vol. 24, p. 508, pl. 31, fig. 1, 1902), called a dwarf, short, squarish form with greater proportional diameter the variety Conradiana. Dimensions. —Lon.+4,-7; alt.+1,-6; semidiam. 3 mm. Occurrence.—Oligocene of the Bowden beds, Jamaica, of the Chipola River and Oak Grove, Florida; Miocene of Duplin County, North Carolina; Pliocene marls of the Cal- oosahatchie, Shell Creek, and Alligator Creek, Florida, and the Waccamaw River, South Carolina. Recent, with a range from Cape Hatteras, North Carolina, to the island of Fernando Noronha, on the coast of Brazil, in five to one hundred and sixteen fathoms.— Dall. Oligocene of Bailey’s Ferry, Florida; Miocene of Curry and the Natural Well, North Carolina; Pliocene of the Croatan beds, North Carolina; and recent from Cuba.— C. U. Museum. Barbatia (Fossularca?) ovalina Dall; Plate V, Figure 2; (Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 630, pl. 32, fig. 18, 1898), from the Oligocene of Bowden, Jamai- ca, has the form of a Vucula, the cardinal margin of a Lzmopszs, and the teeth of an A7vca. Lon. 3.2 mm. 23 AMERICAN East Coast ARCAS 23 Arca lignitifera Aldrich Plate V, Figures 3, 4 Arca ( Barbatia) ignitifera Aldrich, Nautilus, vol. 22, p. 75, pl. 5, figs. 6, 7, Dec. 1908. “Shell small, thin, extremities rounded, moderately convex, beaks small and flattened; surface marked by many radial riblets crossed by irregularly spaced lines of growth; a depressed area running from beaks to base nearly central; valves smooth internally, but showing faint lines corresponding to some of the riblets. Hinge line long, slightly curved; the hinge carries four close-set teeth anteriorly, next a short vacant space, and then ten to thirteen small teeth, larger and more nearly parallel to the hinge line as they approach the posterior. “Lon. 5 mm.; alt. 3 mm. “Locality. Six miles east of Thomasville, Ala., Wood's Bluff horizon.’’—A/drich, 1908. Occurrence.—[Sabine] Eocene of Alabama.—A/arich. Arca Aldrichi Dall Plate V, Figure 5 Barbatia ( Cucullaria) Aldricht Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 630, fig. 19, 1898. “Shell small, elongate, thin, somewhat pointed behind, rounded in front, moderately convex, with low, prosogyrate beaks; cardinal area very narrow and elongated, widest in front of the beaks; surface evenly sculptured by fine equal, flattish radial riblets, sep- arated by narrower grooves and crossed by irregularly spaced impressed lines; inner mar- gin of the valves smooth or slightly fluted in harmony with the ribs, especially behind; beaks in the anterior fourth; hinge-line about two-thirds the length of the shell; hinge anteriorly with four oblique, rather close-set teeth, separated by a wide gap from the posterior teeth, which are about six in number, smaller proximally, and parallel with the hinge-line. Lon. 8.3, alt. 5, diam. 4 mm. ““A single specimen of this interesting shell was obtained, adding a new group to the list of Eocene forms found in the Claibornian. The hinge is somewhat like that of Arca (Cucullaria) Caillati Deshayes, but wants the central vertical denticles. The form is more like that of 4. gracilis, Desh., but wider and more regular.’’—Dal/, 1808. Occurrence —Claiborne sands, Claiborne, Alabama.—Dall. Arca taeniata Dall Plate V, Figures 6, 7 Barbatia (Cucullaria) teniata Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 631, pl. 25, figs. I, Ia, 1898. “Shell thin, elongated, arcuate, mesially compressed, in general inflated; the beaks near the anterior fifth; anterior end rounded, short; posterior higher, produced, and 24 PALAEONTOGRAPHICA AMERICANA 24 bent down; base receding mesially; cardinal area short and wide in front of the beaks, long and narrow behind them, in front smooth or longitudinally striated, behind with a few oblique grooves; sculpture of small, flat, radial ribs arranged in pairs with narrower interspaces, and between every set of two pairs and the next a wider interspace, as if the ribs were quadripartite; these ribs cover all the shell, more sparsely on the posterior dor- sal slope, and are crossed at wide but not perfectly regular intervals by narrow, flat, con- centric ridges; inner margin of the valves smooth, except when modified by the external ribbing; hinge two-thirds as long as the shell, with four rather large oblique anterior teeth separated by a wide edentulous gap from a row of about twenty short vertical teeth, which merge into a group of six or seven oblique posterior teeth, becoming larger distally; the extreme distal teeth in full-grown specimens sometimes break up into irregular gran- ules. Length of adult shell 52, of hinge-line 29, alt. of shell 23, diam. 2t mm.’’—Dadl, 18098. Occurrence.—Pliocene marls of the Caloosahatchie and Shell Creek, Florida, and of the Croatan beds of North Carolina, at Mrs. Guion’s marl pit.—Dad/. Macrodon asperula Dall; Plate V, Figures 8, 9; Dall, Bull. Mus. Comp. Zool. Har- vard, vol. 9, p. 120, 1881; vol. 12, p. 244, p. 8, figs. 4, 4a, 1886; U.S. Nat, Mus., Bull. 37, p- 42, pl. 8, figs. 4, 4a; Bentharca asperula Verrill and Bush, Proc. U.S. Nat. Mus., vol. 20, p. 842, 1898; Barbatia (Cucullaria) asperula Dall, Wagner Free Inst. Sci., Trans., vol. 3, p. 659, 1898, is given by Dall as recent from Fernandina to Yucatan in three hundred and ten to fifteen hundred and sixty-eight fathoms. The name is preoccupied in Arca by Deshayes, An. S. Vert., vol. 1, p. 883, pl. 66, figs. 4-6, 1860. Dall’s species might be called drca paserula. Macrodon sagrinata Dall; Plate V, Figure 10; Dall, Bull. Mus. Comp. Zool. Har- vard, vol. 12, p. 245, 1886; U.S. Nat. Mus., Bull. 37, p. 42, 1889; Barbatia ( Cucullaria) sagrinata Dall, Wagner Free Inst. Sci., Trans., vol. 3, p. 659; Arca (Cucullaria) sagri nata Dall, U. S. Nat. Mus., Proc., vol. 24, p. 508, pl. 31, fig. 2, 1902, is from water eighty fathoms deep northwest of Cuba. Arca profundicola Verrill; Plate V, Figures 11, 12; Verrill, Trans. Conn. Acad., vol. 6, p. 439, pl. 44, figs. 23, 23a, 1885; Dall, Bull. Mus. Comp. Zool. Harvard, vol. 12, p. 245, 1806; Macrodon profundicola Dall, U.S. Nat. Mus., Bull. 37, p. 42, pl. 46, figs. 23, 23a, 1889; Barbatia (Cuculiaria) profundicola Dall, Wagner Free Inst. Sci., Trans., vol. 3, p- 659, 1898; Bathyarca profundicola Verrill and Bush, Proc. U. S. Nat. Mus., vol. 20, p-. 844, pl. 78, fig. 2, 1898, has been found in deep water off the northeastern and southern coasts of the United States. Arca lactocomata Dall; Plate V, Figures 13, 14; Dall, Bull. Mus. Comp. Zool. Har- vard, vol. 12, p. 243, pl. 6, figs. 9, 10, 1886; vol. 18, pp. 433-435, 1889; U. S. Nat. Mus., Bull. 37, p. 40, pl. 6, figs. 9, 10, 1889, is from eighty-two to one hundred and sixty-nine fathoms from Martinique and Barbados. Arca (Barbatia) pteroéssa E. A. Smith; Plate V, Figures 15, 16, 17; Smith, Chal- lenger Rep., Lam., p. 262, pl. 17, figs. 4-4b, 1885; Bathyarca pteroéssa Verrill and Bush, Proc. U. S. Nat. Mus., vol. 20, p. 843, 1898; Arca (Cucullaria) pteroéssa Dall, Bull. Mus. 25 : AMERICAN EAsT Coast ARCAS 25 Comp. Zool. Harvard, vol. 43, p. 399, 1908, was found off Culebra Island, West Indies, and near the Azores and in the North Pacific. Subgenus Noetia Gray Noétia Gray, Syn. Cont. Brit. Mus., 1840. (Dall). Subgenus oétia Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 616, 1898. The Noétias form a distinct division of the Avcas. Dall says the known fossils are all American and the recent species American and Indo-Pacific. The shell is equivalve, the posterior part is separated from the rest of the shell by a distinct umbonal ridge and in A. reversa, the type of the group, is so short that the beaks are posterior. The car- dinal area usually appears twisted on account of its concave anterior part with raised margin and flat posterior part. The ligament is crossed by transverse grooves which usually extend the width of the ligament in front of the beaks but are weaker posteriorly. Behind the ligament isa bare strip of the cardinal area which is usually oblique to the hinge-line, but in 4. veversa it lies between the beaks and the ligament is entirely an- terior. At the anterior end of the hinge and part way between the center and posterior end the teeth are v-shaped. Nearly all the interspaces show a fine interstitial rib. Arca incile Say Plate V, Figures 18, 19, 20, 21, 22, 23, 24, 25 Arca inctle Say, Acad. Nat. Sci. Phila., Journ., 1st ser., vol. 4, p. 139, pl. 10, fig. 3, 1824; Conrad, Fos. Tert. Form., p. 16, pl. 2, fig. 1, 1832; Fos. Med. Tert., p. 56, pl. 29, fig. 5, 1840. Anomolocardia (Arca) incile Conrad, Acad. Nat. Sci. Phila., Proc. for 1862, p. 580, 1863. Anadara incile Meek, Miocene Check List, Smith Misc. Coll. (183), p. 6, 1864. Noetia protexta Conrad, Kerr’s Geol. Rep. N. Car., App. A, p. 19, pl. 3, fig. 5, 1875. Arca (Noétia) incile Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 632, 1898. “Shell transverely rhomboidal, with about twenty-seven ribs; anterior hinge margin compressed and angulated. “Disk prominent from the beaks to the anterior part of the base: ribs with trans- verse granules; those anterior to the middie alternating with very slender and but little prominent lines and with a groove on each: anterior margin longer to the base than the posterior end, and contracted in the middle: series of teeth nearly rectilinear, entire; in- terval between the teeth and the apices with a few transverse lines or wrinkles; a single oblique groove from the apex to a little before the middle, and six or seven narrow ones from the teeth outwards behind the apices: beaks placed very far backward: inner mar- margin crenated: muscular impressions a little elevated, posterior one short: basal mar- gin not parallel with the hinge margin * * * .’’—Say, 1824. In Say’s description anterior and posterior are reversed. Ribs twenty-seven to thirty-two, one specimen has thirty-four; a fine interstitial rib in the interspaces, sometimes wanting near the middle of the shell; ribs close-set on the anterior part of the shell except near the hinge, broader, higher and with wider inter- spaces about the umbonal ridge; posterior ribs with a longitudinal sulcus; beaks very an- terior, elevated; cardinal area long, the portion occupied by the ligament diamond shaped 26 PALEAONTOGRAPHICA AMERICANA 26 and extending backward to a point about half way from the beaks to the posterior ex- tremity of the hinge in the adult, shorter in the young; ligament area with transverse grooves which are stronger in front of the beaks; posterior part of the cardinal area longi- tudinally striated; hinge-line as long or nearly as long as the shell; umbonal ridge angu- lar; shell long and rectangular, anterior margin rounded, ventral nearly straight and de- scending so that the lowest point of the shell is at the posterior end, posterior end usually emarginate and nearly at right angles to the hinge; hinge narrow; line of teeth straight, posterior teeth oblique, anterior teeth vertical except at the end of the hinge, where a few are usually bent at a right angle, as in 4. ponderosa. It is apparent that Conrad’s Moetéa protexta from the Miocene of North Carolina is the same as Say’s A. zncile. The specimen of A. trigintinaria Conrad (Acad. Nat. Sci. Phila., Proc., p. 289, 1862), in the museum of the Academy, is intermediate between incile and limula. It is not a separate species, but rather a variety of zwc/e. It is from the Miocene of South Carolina. A. zmcilis Kerr, Geol. Rep. N. Car., 1875, is a misprint for A. incile. ~~ Dimensions.—Lon.+8,-26; alt.+5,-18; diam. 22 mm. Large valve.—Lon. 45, alt. 30, semidiam. 14 mm. Occurrence.—Miocene of Maryland, Virginia, and North Carolina; near Darlington, South Carolina, at various points near and at the Natural Well, Duplin County, North Carolina; Petersburg, Dinwiddie, York River, and borders of the Dismal Swamp, Vir- ginia, and Choptank, Maryland.—Dall. Miocene of Grove Wharf, Evergreen, Kingsmill, Yorktown, Bellefield and Shackleford, Virginia; Magnolia, North Carolina; Darlington C. H., South Carolina; Tertiary of James River, Virginia—C. U. Museum. Area limula Conrad Plate V, Figure 26; Plate VI, Figures1, 2, 3, 4, 5 Arca limula Conrad, Fos. Tert. Form., p. 15, pl. 1, fig. 1, 1832; Fos. Med. Tert., p. 60, pl. 31, fig. 3, 1845. Noetia (Arca) limula Conrad, Acad. Nat. Sci Phila., Proc. for 1862, p. 580, 1863. Arca (Noétia) limula Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, pp. 617, 631, 659, pl. 31, figs. 14, 14b, 1898. “Oblong, sinuous, rather thin; ribs numerous, crossed by striz, which are equally distinct in the interstices; ribs double on the posterior side where they alternate with fine lines; umbo angulated behind; hinge area narrow, oblique, and transversely striated; basal margin contracted near the middle; inner margin crenate * * *. “This shell has a general resemblance to Arca ponderosa, of Say, but cannot be con- founded with that species.’’—Conrad, 1832. Dall (Wagner Free Inst. Sci., Trans., vol. 3, p. 632, 1898) gives the two following varieties of 4. limula: Arca limula var. platyura Dall Pliocene of the Caloosahatchie and Alligator Creek * * *, 27 AMERICAN East Coast ARcAS 27 Shell with the posterior end of the cardinal border elevated and forming nearly a right angle with the posterior margin of the valves, thus giving the posterior part of the shell a higher and more angular look, which at first seems very distinct. Arca limula var. filosa Conrad Noétia ponderosa Say, var. N. carolinensis Conrad, Proc, Acad. Nat. Sci. Phila., for 1862, p. 290; not Arca carolinensis Wagner, 1847. Arca carolinensis Heilprin, Proc. Acad. Nat. Sci. Phila. for 1881, p. 450. Noétia filosa Conrad, Kerr’s Geol. Rep. N. Car., App. A, p. 20, pl. 4, fig. 3, 1875. Miocene of North Carolina: at Sullivan’s marl-pit, Green Coane, North Carolina, eight miles east of Snow Hill * * *. This variety has more numerous (thirty-five) ribs when adult anda less angular outline than the typical form. * * * A variety analogous to platyura is possessed by all the species of Moétia, but is perhaps more conspicuous in 4. limula * * *, In A. imula there are from twenty-eight to thirty-five ribs. In the long, rounded form they are often narrower and more crowded anteriorly, as in A. incile. Ribs about the umbonal ridge often with a fine riblet like the interstitial rib in the mesial sulcus; in- terspaces crossed by even, concentric lines which give a beaded appearance to the inter- stitial ribs but are less marked on the primary ribs as a rule; posterior strip of the car- dinal area not covered by the ligament; ligament transversely grooved, grooves stronger in front; anterior margin of the cardinal area elevated, posterior rounded; teeth as in A. ponderosa, muscle scars with raised margins; anterior margin of the shell rounded, basal curved or sinuous with the lowest part of the shell usually near the posterior end; pos- terior margin usually with a bend near the hinge. Typical A. mula has a sinuous base and an angle near the top of the posterior margin. It is separated from A. znczle by its larger size, irregular outline, by the angle in the posterior margin and especially by the hinge and position of the beaks. The long, irregular shape and more anterior beaks separate it from A. ponderosa. Specimens from South Carolina, probably from the Pliocene, are, however, closely related to 4. ponderosa. They have a more rectangular outline than typical ma, a relatively longer hinge-line, less anterior beaks, and have little or no bend in the posterior margin. A. limulus Mor- ton 1834 and A. ématu/a Emmons, 1858, are misprints for 4. lémula. Conrad (Acad. Nat. Sci. Phila., Proc. for 1864, p. 211) withdrew his variety carolinensis from the spe- cies ponderosa. Dimensions.—Lon.-+22,-35; alt.+9,-36; semidiam. 19 mm. Occurrence-—Miocene: North Carolina, at Wilmington, New Berne; Virginia, at various points on the York and James Rivers; also in Maryland and South Carolina, and at Heislerville, Cumberland County, New Jersey. Pliocene: De Leon Springs, Florida; in the marls of the Caloosahatchie and Shell Creek; near Brunswick, Georgia; Wacca- maw beds, South Carolina.—Dall. Pliocene of Waccamaw, South Carolina, and the Croatan beds, North Carolina—C. U. Museum. 28 PALAEONTOGRAPHICA AMERICANA 28 Arca ponderosa Say Plate VI, Figures 6, 7, 8, 9, 10 Arca ponderosa Say, Acad. Nat. Sci. Phila., Journ., 1st. ser., vol. 2, p. 267, 1822. Arca contraria Reeve, Conch. Icon., Arca no. 55, 1844. Arca elegans Phil., Zeitschr. Mal., 1847, p. 92 (jide Dall). Not A. elegans Perry, Conchology, pl. 60, fig. 1, 1811; A. elegans Roemer, 1836; A. elegans d’Orbigny, 1844; A. elegans Wood, 1846, or A. elegans de Koninck. Noetia ponderosa H. and A. Adams, Gen. Rec. Moll., vol. 2, p. 537, 1858. Arca (Noétia) ponderosa Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, pp. 617, 632, 633, 659, 1898. “Shell somewhat oblique, very thick and ponderous, with from 25-28 ribs, each marked by an impressed line; interstitial spaces equal to the width of the ribs; umbones very prominent; apices remote from each other, and opposite to the middle of the hinge, spaces between them with longitudinal lines as prominent as their corresponding teeth; anterior margin cordate, flattened, distinguished from the disk by an abrupt angular ridge; posterior edge rounded, very short; inferior edge nearly rectilinear, or contracted in the middle * * *.’’—Say, 1822. In the original description anterior and posterior are reversed. Ribs twenty-five to thirty-two; width of ribs and interspaces not varying much on the different parts of the shell; ribs with a mesial sulcus, sometimes with two sulci; a fine interstitial rib in each interspace, more prominent on the umbonal ridge and some- times indistinct on other parts of the shell; ribs and interspaces crossed by fine, evenly spaced, concentric lines which are stronger in the interspaces; umbonal ridge angular, posterior end produced, posterior margin nearly straight; muscle scars with an elevated border; anterior margin of cardinal area elevated; ligament area longer anteriorly and bounded posteriorly by a narrow uncovered strip extending diagonally backward from the beaks; transverse grooves in the ligament stronger anteriorly; line of teeth curved at the ends, central teeth fine and vertical, anterior teeth larger and v-shaped, posterior teeth large and oblique with smaller, v-shaped teeth toward the center of the line; epi- dermis brownish black. This is a variable species. Specimens from the Pleistocene of Louisiana and South Carolina are mostly short and high like some recent shells from Ft. Barrance, Florida. A valve from the Pliocene of the Croatan beds is unusually long, low and flat, and an- other from the same beds is unusually large, 71 mm. long and 61 mm. high. Neither of these can be placed in the species w/a which is present in the same beds. It is apparent that Reeve’s 4. contraria is the same as Say’s species. Dall places A. elegans in synonymy with A. ponderosa and says, ‘‘There can be little or no doubt that the names of Reeve and Philippi are based on young specimens of this somewhat variable shell.’’ This is one of the best known of the recent Avcas and is easily recog- nized by its heavy shell, interstitial ribs and twisted appearance. Dimensions (long form).—Lon.-+25,-31; alt.4-9,-34; diam. 4o mm. Occurrence.—Pleistocene of Cape May and Atlantic City, New Jersey; of Maryland, near Cornfield Harbor, at Wailes Bluff, on the Potomac River; of Simmons Bluff, South Carolina; and many points on the coast of Florida; recent on the eastern coasts of North 29 AMERICAN East Coast ARCAS 29 America from Cape Cod to Yucatan.—Dal/. Pliocene of the Croatan beds, North Caro- lina: Pleistocene of Georgetown, South Carolina; of Crowley Oil Company and Knapp’s wells, Grand Chenier, and New Orleans, Louisiana: recent from Point au Fer, Louisiana; Galveston, Texas; and Long Key, Cedar Keys and Ft. Barrance, Florida.—C. U. Museum. The Noétias show a variation which reaches an extreme in 4. reversa Gray (Plate VI, Figures 11, 12), from the west coast of tropical America. In A. znecile the shell is long with a long hinge-line and very anterior beaks. In typical démula the beaks are nearly as anterior when distances are measured parallel to the base instead of parallel to the hinge, but the hinge-line is much shorter so that the beaks are a comparatively short distance in front of the center of the hinge. In A. ponderosa both shell and hinge are short and the beaks are opposite the center of the hinge. It is not known below the Upper Pliocene.—Dal/. Pleistocene from New Orleans, Chenier, Knapp’s Wells, Gymnasium Well and Lydia, Louisiana, and of Wailes Bluff, Maryland; recent from Cameron and Point-au-Fer, Louisiana, Galveston, Texas, Ft. Barrance, Florida, and from Aspinwall.—C. U. Museum. Arca triphera Dall Plate XI, Figure 7 Scapharca (Scapharca ) triphera Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 648, pl. 33, fig. 6, 1898. “Shell subequivalve, of moderate size, elongate, not much inflated, subrectangular, with low beaks slightly prosoccelous and marked by a conspicuous wide mesial sulcation; umbones situated at the anterior third of the length; left valve with about thirty-eight rounded subequal ribs separated by narrower interspaces; in the adult about a dozen of the anterior ribs may be squared off and deeply mesially sulcate near the margin, while a few of the ribs on the posterior dorsal slope are narrower, smoother, and more widely sep- arated; transverse sculpture of elevated lines which are somewhat regularly spaced, and 40 AMERICAN East Coast ARCAS 49 in crossing the ribs develop into sharp, thick transverse nodulations; cardinal area very — narrow and with an elevated margin behind, slightly wider in front of the beaks longi- tudinally striate; ends of the hinge-line angular; anterior end bluntly rounded, base par- allel with the hinge-line, posterior end subtruncate, a little produced below; hinge with nu- merous rather crowded subvertical teeth in an uninterrupted series; inner margin of the valves deeply fluted. Lon. of largest valve 28, alt. 14; of younger valve 18, alt. 8.5, diam. 7 mm. ; “The larger valves of this rare species are distorted or worn so that a younger one has been selected for figuring. The most conspicuous feature of the shell is the deep sul- cation of the beaks, which gives them a bilobed appearance.’’—VDal/, 1808. Occurrence.—Pliocene marls of the Caloosahatchie River, Florida.—Dad/. Gabb described Arca Chiriguiensis from the Tertiary of Chiriqui, Central America (Acad. Nat. Sci. Phila., Proc. for 1860, p.567,1861). Later,(Acad. Nat. Sci.Phila., Journ.,2d. ser., vol. 8, pp. 345 and 378), he placed this species, together with fossils from St. Dom- ingo and Costa Rica and Sowerby’s 4. patricia (Quart. Journ. Geol. Soc. Lond., vol. 6, p- 52, 1850) from St. Domingo, all under A. grandis Broderip and Sowerby, (Zool. Journ., vol. 4, p. 365; Reeve, Conch. Icon., Avca no. 4, 1843). Dall, (Wagner Free Inst. Sci., Trans., vol. 3, p. 642), calls the Chiriqui and St. Domingo fossils Oligocene and separates them from gvandis under the name Scapharca (Scapharca) chiriguiensis Gabb. He says that the species ‘‘has about thirty rounded ribs with subequal channelled interspaces, the anterior ribs being granulose or nodiferous, the shell remarkably high, short, solid, and wide. The measurements of a well-grown specimen are: alt. 42, lon. 45, and diam. 44 mm.; the length of the cardinal area is 28 mm. It is one of the spe- cies on the border line between Scapharca and Anadara, the two valves being similarly sculptured and almost equal.’’ Evidently at least two species of fossil shells have been confused here. In the Gabb collection from St. Domingo there are two valves as large and heavy as specimens of 4. grandis from the west coast. These fossils do not show enough variation from the re- cent form to warrant placing them in a separate species. There are a few small valves, the largest 23 mm. long, of a short, well-sculptured Scapharca which are distinct from the young of A. grandis. They are short and high like A. chiriguiensts, but unlike this, the left valve is more nodulous than the right, conspicuous nodules extending over nearly the entire valve, and the ribs of the left valve are square and wider than the interspaces. There are also from St. Domingo two worn valves which resemble the young of 4. grandis in form but appear to be a separate species. The lack of figures of A. patricia and A. chiriquiensis has added to the confusion. Scapharca (Scapharca) halidonata Dall, Plate XI, Figure 8; (Wagner Free Inst. Sci., Trans., vol. 3, p. 646, pl. 33, fig. 24, 1898), from the Bowden beds, Jamaica, and of Cu- racao is of the general type of A. secticostata but is proportionately much shorter. The fossil A. consobrina Sowerby; Plate XI, Figures 9, 10; (Quart. Journ. Geol. Soc. Lond., vol. 6, p. 52, pl. 10, fig. 12, 1850), from St. Domingo also belongs to the group of which A. secticostata is the recent representative. The name consobrina had already been used 50 PALAERONTOGRAPHICA AMERICANA 50 by d’Orbigny for a French fossil (Pal. Frangaise, Terrains Crétacés, vol. 3, p. 209, pl. 311, figs. 4-7, 1844). In the Gabb collection from St. Domingo are shells of another species with the general form of this group but ribbing like that of A. aresta and A. campsa, Arca inequilateralis Guppy; Plate XI, Figures 11, 12; (Quart. Journ. Geol. Soc. Lond., vol. 22, p. 293, pl. 18, figs. 2a, 2b, 1866; Schuchert, U. S. Nat. Mus., Bull., no. 53, p- 56, 1905), from the Oligocene of Bowden, Jamaica, is referred to the group Scap- harca by Dall, who says, ‘This species is closely related to A. Jatidentata Dall, * * * but may be distinguished from it at once by the shorter, more delicate, and much more numerous hinge-teeth of the Jamaica shell. The latter is also thinner and more elegant in sculpture and less inflated. It somewhat resembles the young of A. hypomela Dall and A. floridana.”’ ‘i Scapharca (Scapharca) actinophora Dall; Plate XI, Figure 13; (Wagner Free Inst. Sci.. Trans., vol. 3, p. 647, pl. 33, fig. 26, 1898), from the Oligocene of Monkey Hill, Panama Railway, is a long shell with beaks in the anterior fourth, about forty entire ribs, arcuate base and narrow, attenuated and rounded posterior end. Scapharca (Scapharca) donacia Dall; Plate XI, Figure 14; (Wagner Free Inst. Sci., Trans., vol. 3, p. 649, pl. 33, fig. 13, 1898), from the Oligocene of Bowden, Jamaica, is a small, donaciform shell (6.8 mm. long), with about twenty-four smooth, entire ribs and attenuated posterior end. Dall lists A. auriculata Lamarck; Plate XI, Fig. 19; (An. s. Vert., vol. 6, p. 43, 1819; Reeve, Conch. Icon., 47ca no. 35, pl. 6, 1844), under the section Scapharca and gives its occurrence as follows:—?Oligocene of Bowden, Jamaica; Pliocene of Limon, Costa Rica; Pleistocene of the Antilles; Recent from Key West to Martinique, in fifteen to forty fathoms. A. Deshayestt Hanley; Plate XI, Figures 15, 16, 17, 18; [Ill. Cat. Biv. Shells, p. 157, 1842, (Dall, Moll. Porto Rico, Bull. U. S. Fish Comm. for 1900, vol. 20, pt. 1, p. 461, 1901); Reeve, Conch. Icon., Avca no. 47, pl. 7, 1844] is found recent in the West Indies and has been reported fossil from the mainland of southern North America. Dall lists it recent from Pernambuco, (Wash. Acad. Sci., Proc., vol. 3, p. 141, 1901). It has about twenty-seven narrow, rounded and finely nodulous ribs, the anterior with a me- dian groove; epidermis brown, thick, scaly between the ribs with bristles near the um- bonal ridge. The shell is practically equivalve and is as near dnadara as Scapharca. The young is auriculate behind and has evidently been confused with A. auricudata Lamarck. Dautzenberg, (Mém. Soc. Zool. France, vol. 13, p. 236, 1900), unites the A. hemider- mos Philippi of d’Orbigny, (Hist. Isla Cuba, pt. 2, vol. 5, Moll., p. 345), with Deshayesii. Arca Websteri Pilsbry (Acad. Nat. Sci. Phila., Proc., vol. 62, p. 488, 1910), appears to be a Scapharca, It is from the Oligocene of Haiti. There is also an Avca sp. undet. from the same place, (1. c., p. 489). Section Anadara Gray “Group of A. antigua 1. (Anadara (Gray, 1847) Adams, 1858, in synonymy,+Avomalocardia Adams, 1858, not of Schumacher, 1817). “Shell heavy, trigonal or oblong, inflated, with prosoccelous beaks, with a wide area 51 AMERICAN East Coast ARCAS 51 wholly covered by the ligament and usually with numerous furrows for the resilium forming concentric lozenges; teeth similar, in a long, uninterrupted series, slightly larger and more oblique distally; valves equal and similarly sculptured; epidermis usually pilose and profuse. “The young shell is often and the adult sometimes auriculate behind. The transition to Scapharca s. s. is very gradual and complete.’’—Daill, 1808. Arca subrostrata Conrad Plate XII, Figures 1, 3, 3, 4 Arca subrostrata Conrad, Acad. Nat. Sci. Phila., Proc., vol. 1, p. 30, 1841; Journ., Ist. ser., vol. 8, pt. 2, p. 185, 1842; Fos. Med. Tert., p. 58, pl. 30, fig. 7, 1845. Not Arca subrostrata Sowerby, Quart. Journ. Geol. Soc. Lond., vol. 3, pp. 413, 418, pl. 15, figs. 8, , 1847. a inadtinde Conrad, Am. Journ. Conch., vol. 5, p. 39, pl. 2, fig. 4, 1869. Scapharca (Arca) subrostrata Conrad, Acad. Nat. Sci. Phila., Proc. for 1862, p. 580, 1863. Scapharca (Anadara) subrostrata Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 655, 1898. Arca (Scapharca) subrostrata Glenn, Maryland Geol. Surv., Miocene, p. 385, pl. 104, figs. 2, 3a, 3b, 1904. “Ovate; profoundly ventricose; ribs about 30, little prominent, flat, longitudinally sulcated; posterior side produced, cuneiform; rounded at the extremity; hinge linear in the middle, teeth obsolete, except towards the extremities; within slightly sulcated; cren- ulations of the margin sulcated in the middle. Length 2 inches.’’—Convad, 1841. Shell slightly inequivalve; beaks mesially sulcate; ribs twenty-nine to thirty-two, each rib with a longitudinal sulcus and usually a shallower sulcus on each side of this, dividing each rib into four riblets, sometimes more than four riblets posteriorly; central ribs sometimes nodulous; interspaces usually narrower than the ribs; cardinal area with five to eight concentric grooves; hinge-line short; older shells with central teeth obsolete and distal teeth irregular. In the ribbing this species resembles 4. dodona, but otherwise the two species are distinct. It is evident that Scapharca tenuicardo Conrad, is a syn- onym of A. sxbrostrata. ‘This is one of the species that show the close relation between the sections Scapharca and Anadara. The young has the characters of Scapharca, but the old shell shows some of the characters of Anzadara. It is placed by Dall in the latter group. Dimensions.—t,on.-+-15,-35; alt.++-7,-29; semidiam. 14 mm. Oceurrence.—Miocene of Maryland in Talbot and Calvert Counties, at Calvert Cliffs, Skipton, Centreville, Plum Point, and other localities. A single valve, stated to be from the Miocene of North Carolina, is in the National Museum.—Dad/. Calvert Mio- cene of Chesapeake Beach, 3 miles south of Chesapeake Beach, Plum Point, Truman’s Wharf, White’s Landing, Church Hill, 3 miles West of Centerville, Reed’s Wye Mills, near Skipton.—Glenn. Miocene of Plum Point and Chesapeake Landing, Maryland. —C. U. Museum. Arca elnia Glenn : Plate XII, Figures 5, 6 Arca (Scapharca) elnia Glenn, Maryland Geol. Surv., Miocene, p. 386, pl. 104, figs. 4a, 4b, 1904. 52 PALAEONTOGRAPHICA AMERICANA 52 “Shell large, moderately thick, but slightly elongated, not inflated, with prominent prosoccelous beak; cardinal area wide, with numerous irregular, zigzag, longitudinal grooves, bounded by a single deep curved groove from the beak to the ends of the hinge-line; hinge-line narrow; teeth small, obsolete medially, tending to become irregular at both ends of the series; right valve with about thirty-one low ribs hardly as wide on anterior dorsal slope as intervening spaces, broader and more elevated on posterior dorsal slope; each rib mesially sulcated by a groove with one or more subordinate grooves on either side; growth lines distinct; margin a continuous curve from anterior end of hinge line to posterior end of base, there sharply curved; posterior margin oblique to hinge line; in- terior margin crenulated; dorsal and posterior slopes meet in an angle that becomes rounded near the basal margin. ‘“This species seems to be intermediate between A. sfaminea and A. subrostrata, being perhaps more nearly related to the latter. ‘Length, 60 mm.; height, 48 mm.; diameter, 22 mm.’’—G/enn, 1904. Occurrence.—Choptank Miocene of Jones Wharf, lower bed at Governor Run, 2 miles south of Governor Run, Maryland.—Glenn. Arca clisea Dall Plate XII, Figures 7, 8 Scapharca ( Anadara) clisea Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 657, pl. 33, fig. 25, 1898. Pi renee clisea Glenn, Maryland Geol. Surv., Miocene, p. 386, pl. 105, fig. 1, 1904. ‘Shell large, heavy, inflated, short, with small, high, somewhat prosoccelous beaks, the two halves of the wide cardinal area inclined to one another in the adult at an angle of about forty-five degrees; left valve with about thirty strong, flattened subequal radial ribs with narrower interspaces; in the young the ribs are furnished with small trans- verse nodulations, which gradually become obscure in the adult; the only transverse sculpture is of the ordinary incremental lines; the ribs in the adult are flat topped and rarely show any tendency to mesial sulcation, and when present it appears only on a few of the anterior ribs near the margin; the anterior end is obliquely rounded to the base, the posterior end a little produced basally; the cardinal area is exceptionally wide, with a single impressed line joining the beaks and six or seven concentric lozenges de- fined by sharp grooves; a deep groove also bounds the area; hinge-line straight with numerous small vertical teeth, becoming much larger distally and tending to break up into granules at both ends of the series in the senile shell. Lon. 51, alt. 53, diam. 53 mm. “This shell is apparently related to A. callipleura and A. staminea Conrad, and a larger series of specimens may oblige us to unite all three as varies of a single species. At present, however, the differences seem too great to admit of this course. In A. cal- lipleura the ribs are granulated and triply sulcate, while in the present form they are simple. 4. clisea has no posterior truncation like that figured by Conrad in 4. callz- pleura. A. staminea is more squarely compressed before and behind, with a tendency 53 AMERICAN East Coast ARCAS 53 to incurvation of the posterior basal margin; it is a smaller shell with more posterior beaks, and less roundly inflated. We have a large series of this species from many lo- calities, and these differences characterize them all. The forms are easily differentiated, so far as our present knowledge goes, and therefore are better kept apart. In all the pairs of A. staminea in the collection the right valve is distinctly smaller than and fits into the other, while in A. c/sea the margins meet evenly.’’—Dal/, 1808. Glenn thinks this shell is more closely related to A. zdonea than to any other. Some of the short, high forms of A. staminea approach A. clisea. A left valve from Ev- ergreen, Virginia, which resembles 4. c/zsea is related to A. staminea, but is well rounded instead of angular. The specimen figured is related to zdonea. Occurrence—Chesapeake Miocene of Maryland, and at St. Mary’s River and Cris- field; of Nomini Cliffs, Virginia; and of Walton County, Florida—JDal/l. St. Mary’s Miocene of St. Mary’s River, Crisfield well at depth of 140 feet.—Glenn. Miocene of North Carolina.—C. U. Museum. Arca aresta Dall Plate XII, Figures 9, 10, 1i Scapharca ( Anadara) aresta Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, pp. 638, 655, pl. 33, fig. 2, 1898. “Shell of moderate size and thickness, arcuate below, straight above, with small but prominent prosoccelous beaks, left valve with twenty-seven square-topped, narrow, entire radial ribs, separated by wider interspaces; the ribs on the middle of the shell are somewhat narrower than the others; all are crossed by evenly spaced, moderately prom- inent elevated lines, festooned in the interspaces, and forming small, square ripples on the ribs; both valves similarly sculptured; cardinal area narrow, with elevated margins behind, wider and short in front of the beaks; the portion in front of the beaks is longi- tudinally striated, behind the beaks there are three or four concentric, lozenge-shaped groovings; a single transverse groove usually passes between the beaks; hinge-line straight; teeth in two nearly equal series, overlapping a little proximally, the teeth rather crowded and nearly vertical; base of the valves arcuate, rounded into the anterior end, posterior end a little produced; internal margins of the valves fluted. Lon. 41, alt. 28, diam. 26 mm. “This very neat and distinct species appears to be the most common Ark in the upper or Miocene bed at Alum Bluff.’’—Dal/, 1808. : Ribs twenty-four to twenty-nine, usually twenty-seven; beaks mesially sulcate. The prominent characters of this species are the broad, rounded and festooned inter- spaces, the narrow, square-topped ribs and the unusual form. The anterior and poster- ior extremities are both nearer to the hinge-line than to a parallel line through the low- est point of the base; the posterior portion is often attenuated, but in young specimens this part is relatively broader and more evenly rounded; the greatest inflation is anterior to the middle of the shell. 54 PALAERONTOGRAPHICA AMERICANA 54 Dimenstons.—Lon.+15,-31; alt.+6,-24; diam. 32 mm. Occurrence.—Chesapeake Miocene of Alum Bluff, Calhoun County, Florida.—Dal/. Miocene of the Upper bed at Alum Bluff, Florida——C. U. AZuseum. Arca campsa Dall Plate XII, Figure 12; Plate XIII, Figures, 1, 2, 3 Scapharca ( Anadara)campsa Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 656, pl. 32, fig. 21, 1898. “Shell of moderate size, solid, and heavy, with a straight and angulate upper margin, obliquely rounded anterior, produced posterior, and arcuate basal margin; beaks low, much incurved, mesially impressed, and rather anterior; left valve with about twenty- two narrow ribs separated by wider interspaces, crossed by little elevated, regularly spaced incremental lines; the ribs are not nodulous, the anterior ones are flattish or rarely have a shallow sulcus mesially near the margin; they are subequal, but in speci- mens in which the mesial depression of the valve is especially strong, the ribs included in it are narrower and closer together than usual; hinge-line nearly as long as the shell, angular, but not auriculate distally; the beaks are within the anterior third; cardinal area wider in front, narrow behind, longitudinally striated with a few grooves which cir- cumscribe a ‘stemmed’ arrow-head figure, few of them reaching as far forward as the beaks; teeth in two adjacent series, the anterior shorter with a pronounced thickening of the shell below it, over the vertical face of which the teeth extend rather irregularly or are supplemented by denticular wrinkles; posterior series longer, numerous, vertical, dis- tally much wider, and more or less oblique; interior margin of the valves with strong, short flutings. Lon. 47; alt. 28; diam. 27 mm. “This is quite a peculiar species, the teeth of which recall d7g7xa, while all the other characters of the shell indicate its section to be Axadara, another instance, if one were needed, to illustrate the mutability of the dental forms in this family. It cannot be con- founded with any of our other species.’’—Dal/, 1898. Ribs twenty-one or twenty-two; cardinal area with margin elevated behind the beaks; the mesial sulcation of the beaks passing over the umbo and down to the ventral margin asa broad flattening or sulcation. This shell is distinguished by its wide, rounded interspaces and narrow, square-topped ribs crossed by elevated lines as in A. aresta and by its mesial depression. Ina pair of valves which belong together this de- pression is more marked on the left valve. Dimensions.—Lon.+16,-36; alt.+6,-25; diam. 29 mm. Dimensions of a large valve, lon. 64, alt. 43 mm. Occurrence.—Chesapeake Miocene or upper bed at Alum Bluff, Floridaa—Dad/l. Mi- ocene of the upper bed at Alum Bluff, Florida—C. VU. Museum. Dr. Maury lists this species from the Oligocene of Alum Bluff, but the specimens listed prove to have come from the upper bed. 55 AMERICAN East Coast ARCAS 55 Arca rustica Tuomey and Holmes Plate XIII, Figures 4, 5 Arca rustica Tuomey and Holimes, Pleioc. Fos. S. Car., p. 39, pl. 15, fig. 1, 1857. Not 4. rustica Contejean, 1859 (fide Dall). Scapharca (Arca) rustica Conrad, Acad. Nat. Sci. Phila., Proc. for 1862, p. 580, 1863. Arca crassicosta Heilprin, Wagner Free Inst. Sci., Trans., vol. 1, p. 96, pl. 13, fig. 30, 1887. Arca crassicosta Dana, Man. Geol., 4th. ed., p. goo, fig. 1508, 1895. Scapharca (Anadara) rustica Dall, Wagner Free Inst. Sci., Trans., vol. 3, p. 653, pl. 31, figs. 6, 9, 1898. “A. testa crassa, sub-quadrata, radiatim costata; costis sub-squamosis; latere buc- cali brevioribus, costis crenatis; latere anali carinato, angulato, truncato, costis majori- bus; umbonibus inter se fere contingentibus. “Shell thick, somewhat square, radiately, and unequally ribbed; ribs almost squa- mose; buccal side very short, ribs crenate; anal side carinate, angular, truncate, ribs very large; ligament area narrow, umbones nearly touching. “This fossil is readily distinguished by the coarse ribs and deeply excavated inter- stices on the anal side. The margin is strongly crenulated * * *”’—Tuomey and Flolmes, 1857. “The collection of more material since Professor Heilprin’s publication leaves no doubt whatever as to the identity of this splendid species with that of Tuomey and Holmes. It seems to be characteristic of the southern Pliocene. The beaks are much incurved and distinctly prosoccelous, the cardinal area short and wide in front of them, long and narrow with much elevated margins behind; the anterior part of the area is transversely grooved at right angles to the hinge-line; the posterior part has converging grooves, thus forming three or four concentric triangles. The hinge is composed of a short anterior and long posterior series of subequal vertical teeth vertically striated on their flat sur- faces; there are over forty teeth, of which twelve are anterior; the two series are closely approximated. Many of the specimens have a strong posterior auriculation which is more prominent in the young; one specimen measures thirty-two millimeters on the hinge-line and twenty-eight millimeters below the auriculation. An adult measures fifty-three millimeters long, thirty-six millimeters high, and forty millimeters in diame- ter. The largest valve obtained is seventy-one millimeters long and has fifty-four pos- terior and seventeen anterior teeth. In this specimen there are nine longitudinal grooves, and the three or four middle ones are extended in front of the beaks, contrary to the rule in younger specimens, giving the grooved area as a whole the form of a long, narrow ‘‘stemmed’’ arrow-head. In this valve the hinge-line is sixty millimeters long and the vertical of the beak is ten millimeters from the anterior end. “On the whole, this is one of the finest and most striking species in our whole Ter- tiary fauna.’’—Dal/. Ribs seventeen to twenty-two, large and coarse near the umbonal ridge, smaller and more closely set anteriorly and posteriorly. Several Old World fossil species have been called 4. rustica since Tuomey and Holmes used the name. Dimensions.—(Small valve), lon.+10,-36; alt.-++-5,-29; semidiam. 18 mm. - 56 PALAKONTOGRAPHICA AMERICANA 56 Occurrence.—Pliocene of the Waccamaw beds of South Carolina; and of the Caloos- ahatchie, Shell Creek, Alligator Creek, and Myakka River, Florida.—Dal/. Pliocene of Shell Creek, Florida.—C. U. Museum. Arca catasarca Dall Plate XIII, Figure 6 Scapharca (Anadara)catasarca Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 654, pl. 32, fig. 20, 1898. “Shell elongate, solid, subrhomboidal, with very anterior, high, prosoccelous beaks; right valve with twenty-three strong, narrow, rounded ribs, separated by wider, very deep channelled interspaces; concentric sculpture of incremental lines, which are slightly elevated at regular intervals, and cause over much of the valve the tops of the ribs to appear obscurely nodulous; the ribs on the anterior end, though simple in the young, are sharply mesially sulcate in the adult, those on the posterior dorsal slope lower and more rude than those on the body of the shell; the hinge-line is straight, the cardinal area differs from that of A. rustica only by having but a single transverse groove anter- iorly between the beaks; both valves are similarly sculptured, but no adult left valve was collected; the hinge-line is straight and shorter than the shell; there are about fif- teen anterior and four times as many similar vertical posterior teeth, the proximal ends of the series slightly overlapping; the hinge-line in the specimen figured is forty-six mil- limeters long, the vertical of the beak falls at 8.5 millimeters from the anterior end; in- ner matgins thickened, with short flutings. Lon. 55, alt. 36, diam. 45 mm. “This fine species appears to be rare, and was found only at Alligator Creek * * * The young has much the outline of A. aurzculata, but is not markedly auriculate. It is proportionately shorter than the adult. The species belongs to the same subordinate group as 4. rustica, as is shown by the minor characters. ‘“‘A single broken valve, probably of this species, is among the material from Shell Creek.’’— Dall, 1898. Occurrence.—Pliocene marl of Alligator and Shell Creeks, Florida.—DaJ. Section Cunearca Dall, 1898 “Group of A. tucongrua Say. (Cunearca Dall.) “Thin, trigonal, inflated, with erect beaks; the cardinal area short, amphidetic, equilateral, set off by deep grooves from the rest of the sculpture, smooth or transversely striated, without furrows; hinge-teeth divisible into two series, smaller proximally, larger and more oblique distally, often more or less A-shaped; the right valve smaller; sculp- ture of the two valves obviously discrepant; the epidermis smooth or not pilose.’’—Dad/. Arca initiator Dall Plate XIII, Figures 7, 8, 9 Scapharca (Cunearca) initiator Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 634, pl. 32, fig. 11, 1898. 57 AMERICAN East Coast ARCAS On ~r “Shell small, solid, oblique, with prosogyrate beaks, somewhat impressed mesially near the apices of the valves; right valve ovate-rhombic with twenty strong, rounded, nodulous, radial ribs, separated by wider interspaces; left valve decidedly smaller, with the ribs smooth, squarish, and without nodules, except a few on some of the shorter an- terior ribs; cardinal area wider in front of the beaks, narrower behind them; margins of the valves internally fluted; hinge-line short, with about twenty-two subequal vertical teeth. Lon. (of left valve) 5, alt. 4.7, diam. 5 mm. “This little shell was at first thought to be the young of a larger species, but noth- ing allied to it of a larger size has turned up at any locality in the formation, while its solidity gives ita mature appearance. The cardinal area differs in form from any of the known species in the adult state.’’—Da//, 1808. Evidently the words right and left are interchanged in the original description. More than half of the ligament lies behind the beaks and it does not cover the entire cardinal area, but leaves a broad, uncovered band along the anterior and posterior mar- gins of the cardinal area. There is no sulcation parallel to the umbonal ridge as in A. TNCONLTUL. Dimensions.—(Left valve), lon.+2.5,—4; alt.+1,-4.5; semidiam. 3 mm. Occurrence.—Oligocene of the Chipola beds, Chipola River. Florida.—Dal/. Oligo- cene of Sour Lake, Texas.—C. U. Museum. Arca scalaris Conrad Plate XIII, Figures ro, 11 Arca scalaris Conrad, Acad. Nat. Sci. Phila., Proc. for 1843, p. 324, 1843. Arca scalaris Conrad, Fos. Med. Tert., p. 59, pl. 31, fig. 1, 1845. Arca scalaris Tuomey and Holmes, Pleiocene Fos. S. Car., p. 43, pl. 16, figs. 1, 2, 1856. Scapharca ( Arca) scalaris Conrad, Acad. Nat. Sci., Phila., Proc. for 1862, p. 580, 1863. Scapharca ( Cunearca) scalaris Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p- 634, 1898. “Obliquely rhomboidal, elevated, ventricose, ribs about twenty-three, broad, square, prominent, profoundly and robustly crenate, wider than the interstices, seven on the pos- terior slope, prominent; posterior slope flattened; umbonial slope angulated; summit elevated, narrowed; anterior margin obliquely truncated; anterior basal margin obliquely subtruncated; posterior extremity subangulated; beaks remote; area with transverse slightly impressed lines; cardinal teeth irregular, oblique towards the extremities of the hinge line; within with furrows corresponding to the ribs; margin profoundly crenate. Length two inches; height, one and a half inches * * * “Allied to A. txcongrua Say. The description applies to the left valve only as the opposite one has not yet been found.’’—Conrad, 1843. Dimensions (Small left valve). —Lon.+12,-15; alt.+4,-20; semidiam. 10 mm. Occurrence.—Darlington District, South Carolina.—7womey and Holmes. Miocene of Petersburg, Virginia; of Duplin County, North Carolina, and of the upper bed at Alum Bluff, Florida.—Dall. Miocene of North and South Carolina (young), and of Pe- tersburg, Virginia.—C. 77. Museum. 58 PALAKONTOGRAPHICA AMERICANA 58 Arca scalarina Heilprin Plate XIII, Figure 12; Plate XIV, Figures 1, 2, 3 Arca scalarina Heilprin, Wagner Free Inst. Sci., Trans., vol. 1, p. 94, pl. 12, fig. 29, 1887. Scapharca (Cunearca) scalarina Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 634, 1898. “Shell obliquely rhomboidal, elevated, ventricose, angulated posteriorly, flattened ; anterior end short, evenly rounded; beaks prominent, transverse, about eight, distant; ligament-area diamond-shaped, nearly smooth in the young shell, with delicate transverse lines—in the adult, with a limited number of coarse, sinuous longitudinal lines; hinge- line straight, somewhat more than one-half the greatest length of shell; teeth numerous, somewhat oblique toward either end. “Ribs prominent, about twenty-four, broad, square, robustly crenate, those of the left valve broader than the interspaces, flattened posteriorly, about eight on the anal angulation; those of the right valve of about the same width as the interspaces (the an- terior ones the broadest), with an interstitial secondary rounded rib in the center of the interspace; the two valves unequal, the basal margin of the left valve greatly protruding beyond that of the right; base profoundly crenulated. “Length, 3.3 inches; height, 2.5 inches. ‘ek 3 = [t closely resembles the shell identified by Tuomey and Holmes with Arca scalaris of Conrad * * *, Through the kindness of Prof. Whitfield I have been per- mitted to make a comparison with the type-forms described and figured by Tuomey and Holmes, and find that their shell differs very materially from the Florida fossil. In the first place it is decidedly more oblique, and secondly, the ribs adjoing the posterior slope (on the left valve) are not nearly as broad relatively, nor as flattened, as they are in A. scalarina, the ribs of the left valve are more remotely placed from one another, and lack the pronounced interstitial secondary rib, which is so prominently defined in the Florida fossil. Its place is taken by a hair line, which is present in some of the inter- costal spaces. The characters of the Florida shell are remarkably constant * * * were I as positive of the stability of characters of the Carolina fossil, I should have no hesitation in regarding the two as specifically distinct * * *. As it is, the characters of the two are sufficiently distinct, indeed, fully as well-marked as those which separate the Florida fossil from the recent 47ca ixcongrua of the Southern coast, which may, with much plausibility, be looked upon as its immediate descendant. The recent species agrees more nearly in the general outline of the shell, being upright rather than oblique, but differs in the less width (in the left valve) of the ribs, and in lacking the true inter- stitial rib of the right valve (although an indication of it appears in a faint elevated line), agreeing in this respect with the South Carolina fossil. That the three forms are most intimately related there can be no question, and I believe there is likewise little or no question that all lie on the same line of descent.’’—Hez/prin, 1887. “This magnificent species is the largest and most distinct of the entire group, and so far has been obtained only on the Caloosahatchie River * * *.’’—Dadll. Occurrence.—Pliocene marls of the Caloosahatchie, Florida.—Da//. 59 AMERICAN East Coast ARCAS 50 Arca incongrua Say Plate XIV, Figures 4, 5, 6, 7 Arca incongrua Say, Acad. Nat. Sci. Phila., Journ., vol. 2, p. 268, 1822. Arca incongrua Reeve, Conch. Icon., Arca no. 50, 1844. Scapharca (Cunearca) incongrua Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, pp. 618, 635, 659, 1898. “Shell somewhat rhomboidal, with from twenty-six to twenty-eight ribs, placed nearer to each other than the length of their own diameters, and crossed by elevated, obtuse, equal and equidistant lines, which are altogether wanting on ten rays of the disc of the left valve; apices opposite to the middle of the hinge, distant from each other, with a lanceolate space between them, of which the breadth is about one-third of its length; extremities of the hinge margin angulated; posterior edge rounded; inferior edge rounded, that of the left valve extended a little beyond the regular curve in the middle; anterior margin cordate, flattened; anterior edge nearly rectilinear * * *, “This species, which is very abundant on our coast, strongly resembles A. rhoméea, but, agreeably to the figure in the Encyc. Meth., it differs in the width of the space on the hinge margin, in the width of the spaces between the ribs, and in its more rectilinear anterior edge.’’—Say, 1822. In the original description right and left, anterior and posterior are interchanged. Left valve much the larger; ribs twenty-six to thirty; left valve with all the ribs wider than the interspaces, which are very narrow about the center of the shell; anterior ribs coarse, posterior finer; interspaces widest on the anterior part; ribs with transverse, conspicuous, raised lines which are long and narrow except near the umbo, where they are rounder; ribs of the right valve from the center to the umbonal ridge narrow and nearly smooth; left valve with a shallow sulcus anterior and parallel to the umbonal ridge; ligament covering practically all the cardinal area and bounded by a deep groove; ligament area with faint transverse striations; teeth longer and oblique distally. A. z- congrua shows hardly a trace of an interstitial rib on the right valve. There is a thin light brown epidermis. This is one of the commonest east coast shells. The closely related form 4. drasz/- zana Lamarck; Plate XIV, Figure 8; (An. s. Vert., vol. 6, p. 44, 1819), is smaller than A. incongrua, it is proportionately shorter and higher with a short, abrupt posterior slope and straight posterior margin. The abrupt change from nodulous to smooth ribs on the right valve produces an apparent sulcus on the side of the umbo. The shell from the West Coast figured by Reeve as 4. Brasiliana is referred by Dall to 4. nodosa Wood. Dall says, (Wagner Free Inst. Sci., Trans., vol. 3, p. 635), ““The typical 4. zzcongrna is quite variable in form, and I have not seen specimens which could be unhesitatingly re- ferred to it from older beds than the Pleistocene, or more southern localities, living, than the coast of Texas. Here it is mixed with specimens of the évazz/iana type, towards which the zzcongrua tends to vary. The Costa Rica Pliocene fossils are exactly like bra- ziliana, the Antillean shells also, while varying a good deal, retain the dimensions of bra- eiliana and more or less of its other characters. It is probable that the two forms would 60 PALAKONTOGRAPHICA AMERICANA 60 better be kept apart, at least until more is known.” Dimensions.—Lon.+24,-29; alt.+7,-37; diam. 40 mm. Occurrence.—Upper Miocene of the Galveston artesian well (?); Pliocene of Port Limon, Costa Rica; typical specimens from Pleistocene of Wailes Bluff, Maryland, Sim- mons Bluff, South Carolina, and Brunswick, Georgia; recent from North Carolina south to Texas, and (var. ? dvaztliana) from Texas south and east to Cape Roque and south to Rio, Rio Grande do Sul, San Paulo, and Santa Caterina, Brazil—Dal/. Pleistocene of New Orleans and Grand Chenier, Louisiana, and of Simmons Bluff and Georgetown, South Carolina; recent from Point-au-Fer and Cameron, Louisiana, Galveston, Texas, and from Florida—C. U. Museum. A. brasiliana recent from Aspinwall.—C. U. Museum. Arca alcima Dall Plate XV, Figures 1, 2 Scapharca (Cunearca) alcima Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 635, pl. 31, figs. 5, 7, 1898. “‘Shell of moderate size, short, high, inflated, with elevated prosogyrate beaks; left valve with thirty strong, squarely nodulous, radial ribs somewhat narrower than the in- terspaces, without obvious concentric sculpture, front edge rounded, posterior less rounded and longer, meeting the base at a rather blunt angle, this part of the shell being some- what produced; right valve with twenty-seven less prominent ribs, of which the poster- jor dozen have the nodules obsolete or absent and those on the anterior ribs somewhat less marked than on the other valve; cardinal area short, wide, with the beaks incurved over it; inner margin of the valves sharply fluted; hinge-teeth slightly larger and more oblique distally, in general nearly vertical, close set, and about thirty-two in number, not obviously divided in the center. Lon. 27, alt. 27, diam. 22 mm.; lon. of hinge-line 15 mm. “This is one of those species on the border-line of groups which make it so difficult to divide the Arks into clear-cut sections; it has the hinge, cardinal area, and discrepant sculpture of Cunearca; the valves are slightly unequal, and it seems most properly as- signed to a place in this section. It is obviously a form ancestral to such species as Arca Chemnitzi Phil. (A. bicops Orb.+-A. antillarum Dunker, fide Kobelt,+A. Orbignyt Ko- belt), which is referred to Anomalocardia (—=Anadara) by Ihering, and is found recent in the West Indies. This species, which has been distributed under the (MS.?) name of A. rhombica Rawson, is also inequivalve, with discrepant sculpture, and probably should be referred to this section. “Prom 4. Chemnitzi the present species differs by its larger size, more oblique shape, narrower and more numerous ribs * 7? _Dall, 1898. A. Chemnitzi is figured on Plate XV, Figures 3, 4. Occurrence.—Pliocene marls of the Caloosahatchie at Alligator Creek, Florida.—Dad/. 61 AMERICAN East Coast ARCAS 61 Arca filicata Guppy; Plate XV, Figure 5; (Quart. Journ. Geol. Soc., vol. 22, p. 583, pl. 26, fig. 5, 1866; Schuchert, U.S. Nat. Mus., Bull., no. 53, p. 56, 1905), from Man- zanilla, Trinidad, evidently belongs to Cunearca. It is small, ‘‘rather inequivalve, with about thirty ribs, broader than their interstices, and nodosely crenate, becoming nearly smooth on the disk of the right valve,’’ and the ligament area is wide. Dall (Wagner Free Inst. Sci., Trans., vol. 3, p. 636) calls the beds in which this occurs Eocene. Sca- pharca (Cunearca) cumanensis Dall, (Wagner Free Inst. Sci., Trans., vol. 3, p. 633, 1898) from the Oligocene of Cumana, Venezuela, and an island in Lake Henriquillo, St. Do- mingo, is the species listed by Guppy (Geol. Mag., Oct. 1874, p. 443) as A. tncongrua from Cumana. ‘Shell small, resembling .S. zzcongruwa Say in miniature, but with higher, more prominent, and uncompressed beaks, with the ribs of the posterior slope of the tight valve smooth instead of nodulose; the valve higher and shorter, with the beaks more anterior, and the hinge-line somewhat shorter. Lon. of adult shell 26, alt. 25, diam. 21 mm, * * *.’’—Dall. Section Argina Gray “Group of 4. pexata Say. (Argina (Gray, 1840) Adams, 1858.) “Thin, ovate-oblong, rounded; beaks prosoccelous, with the right valve smaller, the cardinal area opisthodetic, or nearly so, and very narrow, the hinge-teeth in two series —the anterior shorter, usually irregular or broken up, the posterior longer, normal; the epidermis imbricated and profuse; inhabiting salt water.’’—Dad//, 18098. Arca campechensis Dillwyn Plate XV, Figures 6, 7, 8, 9, 10, II, 12, 13 ‘“Pectunculus dense et profunde striatus, ovali figura,’’ Lister, Hist. Conch., tab, 237, fig. 71, 1770; Bay of Campeachy. Arca No. 22; Schroeter, Einleit. Conch., 3, p. 288, 1786. Arca campechensis Gmel., Syst. Nat., 6, p. 3312, 1792. Arca ovalis Bruguiére, Enc. Meth., p. 110, 1792. Arca declivis Solander MSS., fide Dillwyn, 1817. Arca campechensis Dillwyn, Descr. Cat. Rec. Sh., vol. 1, p. 238, 1817 (Syn. partim exclus. ), Ja- maica and Carolina; not of Wood, Ind. Test., p. 46, pl. 9, fig. 28, 1825. Arca pexata Say, Acad. Nat. Sci. Phila., Journ., vol. 2, p. 268, 1822. Arca scapha Ravenel, Cat., p. 5, 1834, 7de Stimpson. Not Arca scapha Lamarck, An. s. Vert., vol.6, p. 42, 1819; Reeve, Conch. Icon., Arca no. 25, 1844. Arca americana (Gray) Wood, Index Test. Suppl., pl. 2, Arca, fig. 1, 1828; 7bzd., ed. Hanley, p. 205, 1856; Tryon, Am. Mar. Couch., p. 179, pl. 37, fig. 470, 1874. Arca americana Reeve, Conch. Icon., Arca, fig. 21, 1844; Holmes, Post.-Pl. Fos. S. Car., p. 19, pl. 4, figs. 2, 2a, 1858. Arca pexata Greene, Mass. Cat., 1833; Gould, Rep. Inv. Mass., p. 95, fig. 60, 1841; Reeve, Conch. Icon., Arca, fig. 22, 1844; De Kay, Nat. Hist. N. Y., Moll., p. 176, p. 12, fig. 211, 1843; Tryon, Struct. and Syst. Conch., vol. 3, p. 255, pl. 126, figs. 46, 47, 1884. Arca campechensis Ravenel, Cat. Coll., p. 5, 1834; Arango, Moll. Cubana, p. 262, 1880. Arca Holmesii Stimpson, S. I. Checklist, p. 2, 1860; Tryon, Am. Mar. Conch., p. 179, pl. 37, fig. 471, 1874. 62 PALAKONTOGRAPHICA AMERICANA 62 Not Arca americana Orb., Moll. Cuba, 2, p. 317, pl. 28, figs. 1, 2, 1853. Scapharca (Argina) campechensis Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, pp. 650, 659, 1898. ‘Shell ovate-heart-shaped, with longitudinal ribs, and crowded transverse striae; margin crenated * * * “Shell about an inch and a quarter long, and an inch and three quarters broad; white, tinged with flesh colour at the margin and summits; it has about twenty- five longitudinal ribs, which are crossed with crowded imbricated striae, and at first sight has more the appearance of a Cardium than of an Arca.’’—Dz/l- wyn, 1817. Shell inequivalve, nearly round to rounded quadrate, with much incurved beaks which nearly touch so that the posterior part of the cardinal area appears lens shaped from above; ribs twenty-six to thirty-seven, square on the right valve, often rounded on the left, especially on the posterior part of the shell; ribs usually as wide as or wider than the interspaces; ribs of the left valve often, and of the right valve sometimes with a median groove, sometimes practically all the ribs of both valves are grooved, some- times little grooving on either valve, the species is very variable in this respect, but the grooving is usually stronger on the left valve; beaks very far forward; hinge-line some- what curved; posterior series of teeth long, teeth oblique distally, v-shaped near the middle of the series; anterior series short, broad and irregular; cardinal area long and very narrow posteriorly, wider and very short anteriorly; margin fluted. Although this species varies widely in form and ribbing it is easily distinguished from other east coast species by its hinge and cardinal area. “This very interesting species, of which the synonymy might be much extended, af- fords an excellent illustration of the effects of environment upon the recent form. Its northern limit is at Cape Cod, where the shell is often large, always coarse, and with a dense hirsute periostracum * * *, As we proceed southward, in this species, as in many other shells, we find the shell becoming less earthy and more porcellanous, the sculpture more neat, the periostracum less profuse, and the general size less. South of Cape Hat- teras the chalky, thin type, common in the north, is seldom if ever found. In the Gulf of Mexico and the Antilles the shell is still smaller than in the Carolinas * * * A somewhat similar series of differences is observable in the Pleistocene fossils, though less pronounced. ““Gmelin’s description was inadequate, and only identifiable by his reference to Lister. The species was elucidated by Dillwyn * * * “The typical A. campechensis is the rounded southern form which Stimpson after- wards called 4. Holmesiz?, as he himself recognized. Say’s description of A. pexata in- cluded all the varieties of our eastern coast, but Gould first described the shell so as to make this name apply more particularly to the somewhat elongated, earthy northern va- riety. Gray’s 4. americana was founded on a very elongated, more porcellanous form, such as is common in South Carolina waters. The study of a large series Of recent spe- cimens, ranging from Jamaica to Cape Cod, obliges me to recognize that no sharp line of discrimination can be drawn between the several varieties. The number of ribs varies 63 AMERICAN Hast Coast ARCAS 63 from twenty-six in the roundest, 4. Holmes, to thirty-five in the most elongated, 4. americana: but the short, round ones often have as many ribs as the elongated speci- mens * * *. The anterior granular series of teeth is much shorter than in A. folepia, and does not extend much in front of the beaks.’’—Dadl/. The synonymy is largely taken from Dall. The references to Lister, Schroeter, Gmelin, Bruguiére and Solander are also given by Dillwyn. Dillwyn’s reference to Lis- ter, Enc. Meth., t. 310, f. 1, is incorrect. The A. ovadzs included in the synonymy is not A? ovalis Gabb, (Acad. Nat. Sci. Phila., Journ., 2d ser., vol. 8, pp..291, 321, pl. 41, figs. 10, 10a), from the Cretaceous of Peru. European fossils have also been named 4. ova/is. Dimensions —Long form, lon.+21,-45; alt.+7,-50; semidiam. 23 mm. Round form, lon.+15,-35; alt.+5,-38; diam. 36 mm. Occurrence.—‘‘The species does not descend below the uppermost Miocene, if, in- deed, any of the specimens are so old. I have only identified it with certainty from the Pleistocene of Georgia, of Simmons Bluff, South Carolina, of New Jersey, and southern New England.’’—Dall. Pleistocene of Grand Chenier, Pumping Station no. 7, and New Orleans, Louisiana and Georgetown, South Carolina; recent from Cameron and Point- au-Fer, Louisiana; Galveston, Texas, Mobile, Alabama, Ft. Barrence, Florida, and from South Carolina.—C. U. Museum. Scapharca (Argina) tolepia Dall; Plate XV, Figures 14, 15; (Wagner Free Inst. Sci., Trans., vol. 3, p. 649, pl. 33, figs. 7, 8, 1898), from the Oligocene of Rio Amina, St. Domingo; Bowden, Jamaica, and Cumana, Venezuela, is smaller (28 mm. long) than 4. campechensis, is much more inflated and rotund and has finer and more nodulose sculp- ture. It has about thirty-four ribs. Dall places in synonymy with his species the A7ca pexata listed by Guppy, (Geol. Mag., Oct. 1874), fossil from Caribbean beds. Guppy also listed A. fevata Say from St. Domingo and Cumana in Quart. Journ. Geol. Soc. Lond., vol. 22, pp. 575, 576, 1866. Among fossils from. St. Domingo in the C. U. Mu- seum there are specimens belonging to several small, inflated species varying from 47gina to section Scapharca. Section Bathyarea, Kobelt “Group of A. pectunculoides Scacchi (Bathyarca Kobelt, 1891.) “Shell small, usually abyssal, inflated, with prosogyrate beaks and a rather narrow but long furrowed area, the hinge-margin nearly or quite as long as the shell; teeth few, oblique, in two series, often separated by a wide gap in the center; the right valve smaller, the sculpture of the two valves often very discrepant; epidermis usually imbri- cated. “These small deep-water Arks go back to the Eocene in time and form a very rec- ognizable group, related to Scapharca as Lissarca is to Barbatia.’’—Dall. Scapharca (Bathyarca) Hendersoni Dall; Plate XVI, Figure 1; (Dall, Wagner Free Inst. Sci., Trans., vol. 3, p. 653, pl. 33, fig. 9, 1898), from the Oligocene of the Bowden beds, Jamaica, is very small (2 mm. long), ‘‘much inflated, the hinge-line as long as the 64 PALAEONTOGRAPHICA AMERICANA 64 shell, which is of a rounded triangular form, with rather prominent prosoccelous beaks; left valve with fine, elevated, rounded concentric lines, crossed by closer, less prominent, and finer radial lines; in the right valve, as usual in this section of the genus, the radial sculpture predominates over the concentric, the latter though present being inconspicu- ous; cardinal area moderately wide, the beaks being nearly medial, the surface of the area longitudinally striated; hinge with about five nearly vertical anterior teeth separated by a wide unarmed gap from six or seven smaller, more oblique posterior teeth; margin of the valves thin, entire, or microscopically crenulated; the inner edges of the adductor scars slightly raised above the inner surface of the valve * * *. It resembles A. pec- tunculoides Scacchi and A. glomerula Dall, of the recent fauna, but is smaller, more in- flated, and more triangular than either of them.’’ Scapharca (Bathyarca) Spenceri Dall; Plate XVI, Figures 2, 3; (Dall, Wagner Free Inst. Sci., Trans., vol. 3, p. 652, pl. 32, figs. 16, 24, 1898), from the Pliocene of Tehuan- tepec, is large for the section, (18 mm. long), “inflated, ovate, with prominent prosocce- lous beaks; left valve with fine, rounded, concentric elevated lines, close set, and with very narrow interspaces, which show fine, close radial striae, some of which on the an- terior end of the shell are more prominent; right valve with fine, close-set radial ribs, coarser on the middle of the shell, separated by narrower, sharp, channelled grooves; transverse sculpture of evenly spaced, low, sharp elevated lines which cross the ribs with- out becoming much thickened; cardinal area very narrow behind, wider but not distinctly limited in front, the cardinal margin elevated anteriorly, with seven or eight concentric grooves mostly behind the umbones; ends of the hinge angular behind; the teeth in two series hardly separated, eight to twelve in front, ten to fourteen behind, not crowded, smaller mesially, larger and more oblique distally, the anterior series somewhat irregular; inner margin of the valves with fine crenulations, stronger in the left valve, the outer edge almost or quite entire.’ Scapharca (Bathyarca) glomerula Dall; Plate XVI, Figures 4, 5; ( Dall, Bull. Mus. Comp. Zool. Harvard, vol. 9, p. 121, 1881; vol. 12, p. 241, pl. 8, figs. 9, 9a, 1886; U.S. Nat. Mus., Bull. 37, p. 42, pl. 8, figs. 9, 9a, 1889; Wagner Free Inst. Sci., Trans., vol. 3, p- 659, 1898), recent from Hatteras to St. Vincent in one hundred to six hundred and eighty-three fathoms, is similar in general shape, size and sculpture to 4. pectunculoides, but is shorter and higher; the hinge is straight with from fifteen to seventeen stout nearly vertical teeth, usually in a continuous series, those at the ends of the series oblique; the sculpture of the two valves is different, the radiating sculpture stronger on the right valve; the radiating sculpture appears inside the shell within the margin in a series of small ridges, generally with the same level as the rest of the interior, but sometimes ris- ing into little tubercles, and separated by rather deep, short, narrow depressions, which do not extend far inward nor over the smooth margin. The dimensions of 4. glomeruia are: lon. 5.75, alt. 5.0, diam. 5.0; lon of hinge-line, 4.25 mm. Dall places Arca (Scaph- arca?) inaequisculpta EK. A. Smith, (Challenger Rep. Lam., p. 267, pl. 17, figs. 8-8c, 1885), from deep water off Culebra Island, West Indies, in synonymy with this species. Scapharca (Bathyarca) polycyma Dall; Plate XVI, Figures 6, 7; (Dall, Bull. Mus. 65 AMERICAN East Coast ARCAS 65 Zool. Harvard, vol. 9, p. 122, 1881; vol. 12, p. 241, pl. 8, figs. 3, 3a, 1886; U. S. Nat. Mus., Bull. 37, p. 42, pl. 8, figs. 3, 3a, 1889; Wagner Free Inst. Sci., Trans., vol. 3, p. 659, 1898), recent from Barbados and Grenada, has the dimensions: lon. 9.75, alt. 6.0, max. diam. 5.0; lon. of hinge-line, 6.0 mm. It is ‘‘slightly inequilateral, nearly equivalve, moderately evenly inflated, whitish, with little or very fugacious epidermis; sculpture very remarkable, consisting, first, of very even, broad, rounded, regular, concentric waves (twelve or thirteen in number), separated by sharp, deep grooves. In dead or worn shells these waves are smooth, or nearly so, but in perfectly fresh (and especially young) shells on the surface of the broad slightly flattened waves may be seen what look like two rows of subcylindrical, slightly irregular grains of sand, arranged side by side, with their longer axes radiating from the beak; these granules, if so they may be termed, are really hollow, and are the thinnest possible bubbles of shelly matter which leave, when rubbed off by any slight friction, a couple of zigzag slightly elevated lines where their bases were fixed to the shell; a very slight friction will obliterate this, and then the shell will be nearly smooth * * *; the narrow furrow for the ligament goes straight across to the margin from the beak (which is nearly opposite the middle of the hinge- line) instead of obliquely * * *.’’ Arca pectunculoides ‘Scacchi; Plate XVI, Figures 9, 10, 11; (Scacchi, Not. Conch. foss. Gravina zz Ann. Civ. due Sicil., vol. 6, p. 82, 1834; Broegger, Norges Geologiske Undersoegelse, no. 31, pl. 13, figs. 17a, 17b, 1901; var. orbiculata Dall; Plate XVI, Fig- ure 8; Dall, Bull. Mus. Cornp, Zool. Harvard, vol. 9, p. 121, 1881; vol. 12, p. 240, pl. 8, fig. 5, 1886; U.S. Nat. Mus., Bull. 37, p. 42, pl. 8, fig. 5, 1889; var. crenulata Verrill, Trans. Conn. Acad., vol. 5, p. 575, 1882; Scapharca (Bathyarca) pectunculoides Dall, Wagner Free Inst. Sci., Trans., vol. 3, pp. 619, 659, 1898), belongs to Bathyarca. Its range is given by Dall as from Norway to St. Vincent. It is a well-known European species and is found as a fossil. The shell is thin, with fine radiating and concentric lines; left valve slightly larger; cardinal area wider in front of the beaks; ligament oc- cupying only the posterior part of the cardinal area; teeth oblique, in two series, with a gap opposite the beaks; anterior part of the shell with a shallow sulcation extending toa notch in the ventral margin; inner margin smooth. Dall says that the American specimens are shorter and rounder than those from far- ther east in the Atlantic sea-bed and the Norwegian and Arctic seas. He described a nearly round variety from the Gulf of Mexico as variety orbiculata. ‘Arca grenophia Risso may be this species, but it was not figured, and the description is quite insufficient. Arca pectunculotdes var. crenulata Verrill, appears to have the form of var. orbiculata, the teeth of the Gulf specimens above mentioned, the marginal crenulations of glomerula, and the sculpture of the type of Jectunculoides,’’—Dall. Arca glacialis Gray; Plate XVI, Figures 12, 13, 14; (Gray, Parry’s First Voyage, Supp. to App., p. 244, 1824; Bjoerlykke, Norges Geologiske Undersoegelse, no. 25, p. 69, fig. 1, 1898; Broegger, |. c., no. 31, p. 120, pl. 6. figs. 1-4, 1901; Friele and Grieg, Nor- wegian North-Atlantic expedition, vol. 7, Mollusca 3, p. 19, 1901), is found recent in the Arctic seas and has been reported south to New England. It is also found in the Pleis- 66 PALAEONTOGRAPHICA AMERICANA 66 tocene. It has a thin shell, evenly rounded in front and produced behind with an oblique posterior margin; surface with numerous fine radiating lines; hinge-line short; teeth small, with a gap opposite the beaks; cardinal area wider in front, narrower behind, with araised margin; posterior part Of the cardinal area with several fine, close-set longitu- dinal grooves; inner margin smooth. Bathyarca abyssorum Verrill and Bush; Plate XVI, Figure 16; (Verrill and Bush, Proc. U. S. Nat. Mus., vol. 20, p. 843, pl. 76, fig. 9, 1898), was found in 1825 to 1859 fathoms, off Delaware Bay. A single specimen of a form related to fectunculoides, from a depth of 27 fathoms, Gulf of Maine, was named Bathyarca anomala by Verrill and Bush, (Proc. U. S. Nat. Mus., vol. 20, pp. 843, 844, pl. 77, fig. 8, 1898); Plate XVI, Figure 15. It is not Avca anomala Reeve, (Conch. Icon., 47ca no. 9, pl. 2, 1843); Arca anomala Blake and Hudleston, (Quart. Journ. Geol. Soc. London, vol. 33, p. 398, pl. 35, fig. 7, 1877); or Arca anomala ad’ Hichwald, [Naturhist. Skizze, p. 211, (Lethaea Rossica, vol. 3, p. 78, pl. 4, fig. 12, a, b, c, 1853)]. The Bathyarca might be called Arca (Bathy- arca) Verrillbusht. Arca (Scapharca) culebrensis EK. A. Smith; Plate XVI, Figures 17, 18, 19; (Challenger Rep., Lam., p. 268, pl. 17, figs. 9-9b, 1885), is similar to the variety septentrionalis of A. pectunculoides and was obtained off Culebra Island, West Indies, in 390 fathoms. Cretaceous Species Barbatia Carolinensis Conrad, (Kerr's Rep. N. Car., App. A, p. 4, pl. 1, fig. 11, 1875; Tryon, Struct. and Syst. Conch., vol. 3, p. 254, pl. 127, fig. 79), is from the Cretaceous of North Carolina. It is not A. carolinensis Wagner, 1847. Barbatia lintea Conrad, (1. c., p. 4, pl. 1, fig. 12), is also from the Cretaceous of North Carolina. Dall states that it is not Arca lintea Conrad, Dead Sea Expedition, 1852. Barbatia lineata Tryon, (Struct. and Syst. Conch., vol. 3, p. 254, pl. 127, fig. 65), and Barbatia lineata Meek, (U.S. Geol. Surv. Territories, vol. 9, p. 78; 1876), are misprints for the former species, not Arca lineata Goldfuss. Conrad also described a Czbota lintea from the Cretaceous of Mississippi, (Acad. Nat. Sci. Phila., Journ., 2d. ser., vol. 3, p. 328, pl. 34, fig. 11, 1858.) Dall, (Wagner Free Inst. Sci., Trans., vol. 3, p. 615), includes Memodon Conrad, (Am, Journ. Conch., vol. 5, p. 97, 1869), in the subgenus Barbatia. The following Cre- taceous species have been referred to Memodon by Whitfield, (U. 5. Geol. Surv., Mono- graphs, vol. 9, pp. 83-86, 1885), Johnson, (Acad. Nat. Sci. Phila., Proc. for 1905, vol. 57, D. 9) and Weller, (Geol. Surv. N. Jersey, Cret. Pal., pp. 385-391, 1907):—Arca (Mac- rodon) Eufalensts Gabb, Acad. Nat. Sci. Phila., Journ., 2d. ser., vol. 4, p. 398, pl. 68, fig. 39, 1860, from New Jersey, Georgia, Alabama, Mississippi and Arkansas; 77igonarca eufalensis Conrad, Am. Journ. Conch., vol. 3, p. 9, 1867—=Nemodon conradi Johnson, 1905, from New Jersey; Leda angulata Gabb, Acad. Nat. Sci. Phila., Proc. for 1860, p. 95, pl. 2, fig. 12=Nemodon angulatum Gabb, Acad. Nat. Sci. Phila., Proc. for 1876, p. 316, from New Jersey; Memodon brevitrons Conrad, Kerr’s Geol. Rep. N. Car., App. A, p. 4, pl. 1, fig. 15, 1875, from New Jersey, North Carolina and Mississippi. This last is not Arca brevifrons Sowerby, Zool. Soc. London, Proc. for 1833, p. 22, or Arca brevifrons EEE EEO 67 AMERICAN East Coast ARCAS 67 Conrad, Dead Sea Expedition, p. 215, 1852. The preceding species is not Arca angulata King, Zool. Journ,, vol. 5, p. 336, 1831. Weller, (Geol. Surv. N. Jersey), has referred the following New Jersey Cretaceous species to Arca:— Cibota obesa Whitfield, U.S. Geol. Surv., Monog., vol. 9, p. 93, pl. 11, figs. 30, 31, 1885; not Arca obesa Sowerby, Zool. Soc., Proc., pt. 1, p. 21, 1833; Reeve, Conch. Icon., Arca no. 3, 1843. Arca uniopsts Conrad, Acad. Nat. Sci., Phila., Journ., 2d. ser., vol. 2, p. 275, pl. 24, fig. 17, 1853—Czbota uniopsts Whitfield, U. S. Geol. Surv., Monog., vol. 9, p. 92, pl. 11, figs. 32, 33, 1885. Arca rostellata Morton, Synop. Org. Rem. Cret. Gr. U. S., p. 64, pl. 3, fig. 11, 1834—Cibota rostellata Gabb. Arca quindecemradiata Gabb, Acad. Nat. Sci. Phila., Proc. for 1860, p. 95, pl. 2, fig. 2. Weller places in synonymy with this species Czbota multiradiata Gabb, 1. c., p. 95, pl. 2, fig. 1; Avca altirostris Gabb, Acad. Nat. Sci. Phila., Proc. for 1861, p. 325; Cucullaea transversa Gabb, 1. c., p. 326, and Cucullaea gabdi Johnson, Acad. Nat. Sci. Phila., Proc. for 1905, p, 8. Nemoarca cretacea Conrad, from the Cretaceous of New Jersey, likewise Avca Saffordit Gabb, from the Cretaceous of New Jersey, have sometimes been classed as Avcas. Weller places them in Vemoarca and Areviarca respectively. The former is not Arca cretacea d’Orbigny. A number of Mesozoic species from the interior states and Texas have been classed as Arcas. The Cucullaeas have often been called Avcas. Of Eocene species Dall says, ‘‘A. gigantea Conrad is probably identical with Cucullaea ono- chela Rogers. Noétia pulchra Gabb, from the Eocene of Texas, 1860, is 7rinacria decisa. There is an A. pulchra of Sowerby dating from 1824.’’ The following species are undescribed, described from incomplete specimens, etc. :— Eocene.—In the Report on the Geology of South Carolina, 1848, pp. 156, 161, 210, Tuomey named an undescribed species A. obligua T. It may have been figured in the unpublished plates mentioned in the preface. The name was used by Portlock in 1843, in the Report on the Geology of the County of Londonderry, for a Paleozoic fossil. It has also been used for a South American fossil, and for recent shells by Reeve and Philippi. Eocene.—In the Acad. Nat. Sci. Phila., Proc. for 1852, p. 194, 1854, Tuomey de- scribed a species from North Carolina as follows: ‘‘ARCA CANCELLATA: shell thin, very inequileratal, cancellated by radiating lines and approximating transverse lines; umbones prominent; beaks close; hinge-line slightly curved; posterior margin rounded, com- pressed; anterior margin much contracted. “Dimen. Length 2.5 in.; br. 3.5 in.’’ It was not figured and the name is preoccupied by Gmelin, Syst. Nat., 6, p, 3308, 1792. In180g9 Martin used the name Arcites cancellatus for a British fossil which Sowerby in 1824 called Arca cancellata. 68 PALAEONTOGRAPHICA AMERICANA 68 Oligocene.—In the 16th Ann. Rep. of the State Geologist of Indiana, p, 414, 1889, “ Arca acuminata, Vicksburg Group, Mississippi’’, is given in a list of specimens in the state museum. There is a recent Arca acuminata Krauss from South Africa, (Stidafrikani- schen Mollusken, p. 14, pl. 1, fig. 11, 1848). Oligocene.—A. ovonlensis Gabb, Acad. Nat. Sci., Phila., Journ., 2d. ser., vol. 8, p. 346, pl. 44, fig. 21; Dall, Wagner Free Inst. Sci., Trans., vol. 3, pt. 4, p. 658, is from Panama and Costa Rica. Avca (Anadara) Pennelli Gabb, Am. Phil. Soc., Trans., 2d. ser., vol. 15, p. 254, 1873, and Arca multilineata Gabb, 1. c., p. 254, from St. Domingo, were not figured. Dall lists them as Oligocene. Miocene.—A. maxillata Con., Acad. Nat. Sci. Phila., Journ., vol. 6, p. 264, 1831, from Maryland, was briefly described and was not figured. The specimen was a cast. Miocene.—In the Second Bulletin of the Proc. Nat. Institution Promotion Sci., p. 181, 1842, Conrad lists A. depleura Conrad together with A. sudbrostrata from a locality in Maryland. On p. 183 it is listed from another locality and spelled dip/euva. Appar- ently it was never described and doubtless isa synonym of some Of Conrad’s other species. Miocene.—Among the Galveston deep well fossils Professor Harris found specimens most nearly like the west coast 4. /abiata and he called them Arcaicucullosdes:Contadtse.ccw.c5.ssaesce eee seesc cence eee se eee ene ese eee eee eee eee 13 Jackson Eocene of Texas. An unusually large specimen, showing the serrated umbonal ridge. With age the ribs become more divided except on the posterior slope, where they tend to disappear, leaving the shell nearly smooth. g. Arca cuculloides Conrad; Jackson Eocene of Louisiana, one mile above Gibson's Landing. To show the well-sculptured, simpler ribbed young. The posterior rib- bing is observed by the light. 10. Interior of the same, enlarged. To show the entire teeth and crenulate margin of the voung. 11. Arca cucullotdes Conrad; Jackson Eocene of Jackson, Mississippi. Adult, with ir- regular teeth. This figure shows the characteristic cardinal area of Ca//oarca with close, even grooving. 12. Exterior of the same. at PALZONTOGRAPHICA AMERICANA VOLUME I., PLATE II. 72 PALAEONTOGRAPHICA AMERICANA a PLATE II ! ; FIGURE ; = ‘.Paiews 1, Arca ggiila Heilptty.ccis.iteee on ee Pee FO at crane eee eee 10 : After Heilprin. 2. Arca aguila Heilprin; ‘‘Caloosahatchie beds; lon. 33.5 mm’’; after Dall. 3: Area. Bomdentainta Dall: aiiciuns0ts class obec: ovnet. tse bedeey te phoeeees apeeaeeeeS eeaeae ne p orn “Oligocene of Bowden, Jamaica; 11 mm/’’; after Dall. - 4. Arca barbata Lanne. .. 0 i6cieete ce Matter cunt avelisnpdo cus sers us -4sceesta-gatheenahiaetaey Tago a Be Recent from the Mediterranean. 5. Arca barbata Linné; recent from the West Indies; left valve;x2. This is the form common in the West Indies enlarged to show the grouping of the ribs. 6. Interior of the right valve; x 2. 7. Umbonal view of the same, natural size. Most of the ligament is'broken off. It did not extend ahead of the dark line just behind the beaks, though in larger indi- viduals it may extend farther forward. Bi Arca. cuculloides Contad..ccidessc-ouesanauestuesesan eae teas eee eee ean meee ate chen peceenees 13 Jackson Eocene of Texas. An unusually large specimen, showing the serrated umbonal ridge. With age the ribs become more divided except on the posterior slope, where they tend to disappear, leaving the shell nearly smooth. 9. Arca cuculloides Conrad; Jackson Eocene of Louisiana, one mile above Gibson's Landing. To show the well-sculptured, simpler ribbed young. The posterior rib- bing is observed by the light. 10. Interior. of the same, enlarged. To show the entire ve and crenulate margin of the young. 11. Avca cuculloides Conrad; Jacks& Eocene of Jackson, Mississippi. Adult, with ir- regular teeth. This figure shows the characteristic cardinal area of Ca//oarca with close, even grooving. 12. Exterior of the same. SI PALZONTOGRAPHICA AMERICANA VOLUME I:, PLATE II. 2 7 : os nee RG Te Te se, Qt eae 4 F = ; i i ; : 74 PALAEONTOGRAPHICA AMERICANA 74 PLATE III FIGURE PAGE L. Arca mussissippiensts: CONTAC. 2... awn alelreenineienaeenaseeemeeeresene eer =se rr RAPED op OHONE HORE DAC 14 Vicksburg Oligocene of Vicksburg, Mississippi; 2; oblique view to show the cardinal area. Exterior of same; X 2. 2 3. Interior of the same; X 2. 4. Arca mississippiensis Conrad; Vicksburg Oligocene of Vicksburg, Mississippi. This is close to A. marylandica. iS. Arca marylandsca Conradnce tes-wancncetnoscaccetsaneecasacet erase toate ate ee ee eee eee 14 Oligocene of Bailey’s Ferry, Florida; form with two-angled posterior part. The ribs of the posterior slope are inconspicuous, in contrast to the coarse posterior ribs of A. candida. 6. Arca marylandica Conrad; Oligocene of Bailey’s Ferry, Florida; another form of this species. 7. Arca marylandica Conrad; Oligocene of Bailey’s Ferry, Florida; interior of an ir- regular specimen, showing the close grooving of the cardinal area. 8... Arcacartila Heil prin...... iets snty eescels deo ae oeteees dee wesside hie et ee sees toe eee 15 “Oligocene of Tampa silex beds; 47 mm.’’ after Dall. 9. Arca arcula Heilprin; after Heilprin. : 10, Avca phalacra, Walls... Kose ccossnecuess os cosseeseeeias meee eae ese seec cece eee ee eae eee 16 “Oligocene of Oak Grove, Florida; 23 mm.’’; after Dall. It: Arca candida: Gim@liiti:iccicicec mawcteynesiceoso.s aciecuainaceasnse serene eeeeene eater ee meteors 16 Recent from Santo Domingo. This shows the character of the anterior, cen- tral, and posterior ribs. 12. Arca candida Gmelin; recent from Santo Domingo; interior of a shorter form. 13. Arca trregularis Dallesoesccssc acess soaps a Cabibdehaponeeten Sc hee EO eee eee 17 ‘Pliocene of the Caloosahatchie marls; 52 mm.’’; after Dall. Since the name trregularis is preoccupied this species has been renamed A. caloosahatchiensis. 14, 15. Arca -nodulosa Muller’. soccaceceu, o- ssossume ese Penman An paeeeesenenenecsne icbSocbospnocc: 31 Claiborne Eocene of St. Maurice, Louisiana. The posterior margin is broken. Arca. Lesmeura Da ei cckonsea ceed ne eas ea des ae es esas eee ts cece EEE REECE EEE ee 32 Oligocene of Vicksburg, Mississippi. This shows the double, beaded ribs of the left valve. Interior of the same. Arca Lesueurt Dall; Oligocene of Vicksburg, Mississippi; showing the beaded an- terior and smoother central ribs of the right valve. Arca Lesueuri Dall; Oligocene of Vicksburg, Mississippi. This shows the anterior sculpture as fig. 12 shows the posterior. Arca Lesueuri Dall; Oligocene of Vicksburg, Mississippi; a Jarge right valve. Arca latidentata Dall.............. ROE TC Ec onnrcuent ocd entbeeasmenescnenanm, oae=ocenasceccsoc 33 Oligocene of Bailey's Ferry, Florida; old. Anterior end of the same; figured to show the convexity of old individuals. Arca latidentata Dall; Oligocene of Bailey’s Ferry, Florida: adult, slightly reduced, Arca latidentata Dall; Oligocene of Bailey’s Ferry, Florida; slightly reduced. AAR CLRLY ED. NOFA oeeoanansoce someneaeaqnGan sia sans sooo jossdaoposednoveeSdavdbousadeovodSse cones oooES: 34 “Oligocene of Alum Bluff, Florida; 20 mm.’’; after Dall. : Airca iy ponzel aw alll sete ceisen- i eqsecissielectee see Crier e eee ee eee eee eee eee 34 Oligocene of Bailey’s Ferry, Florida. Interior of the same. Arca hypomela Dall; Oligocene of Bailey’s Ferry, Florida; individual with narrow ribs. Umbonal view of the same. Arca emOSa: SY isc coca oe one meme see eel cre se ee ere sine ite late sagt arse eee Ree esate ee 35 Miocene of Kingsmill, Virginia; a valve with arcuate ventral margin. Arca lienosa Say; Miocene of North Carolina; a valve with the ventral margin nearly parallel to the hinge. Interior of the same. PALZHONTOGRAPHICA AMERICANA VOLUME I., PLATE VII Wgei C4 fh + hi Pree SETH) % EAA T AVN é TBA y? 82 A 2 $ FIGURE ; 1. (Artatrentiaria) Gap py ocd wcadseo toca agen coh een Bi ete <> resegs eee Edel i , “Exterior of left valve. Verses Trinidad’; after Guppy. 2.3 Arca trinitarja Guppy; ‘‘Pasterior view of the shell with the Ma ke ‘Guppy. 3. _Arca-centrota: Guppy. sa. marsgpdueener ones Somme es Naensare ae ree Laie “Pliocene, Trinidad’; after Guppy. 11 : wate A. Arca’bisiicata, Latiarcl..2.. «cher» " rir : alte ‘ f - ce » . “e < 24 i a 4 ’ 1 . ; v — 5 , , 4 Je ’ 84 PALAEONTOGRAPHICA AMERICANA 84° PLATE VIII FIGURE R , PAGE Tey PUY CR DIOL AGLA ARO SELS em asytas ences seers asin asieecessaeueasesseseaseoeecuse cee eas ene escenener 36 After Rogers. 2. Arca protracta Rogers; after Rogers. 3. Arca secticostata REEVE eerie ee so aihadacishes ciemetas SeadeGaabE a aS Se 36 Recent from Florida; interior of a right valve. The fluting of the ventral mar- gin is obscured by the illumination. 4. Arca secticostata Reeve; recent from Florida; umbonal view. 5. i : eles PALAONTOGRAPHICA AMERICANA VOLUME I., PLATE VIII. 86 PALAEONTOGRAPHICA AMERICANA 86 PLATE Ix FIGURE PAGE i Arca santarosana: Dalle s.maceoececicetencrscieassasesddewenetee ancee sere ete etter ee 38 Oligocene of Oak Grove, Florida. The posterior ribs are obscured by the illu- mination. 2. Interior of the same. 3. Arca santarosana Dall; Oligocene of Oak Grove, Florida; right valve. 4... Arta staminata Dalles ic. saecccessnecansterenesoadses1seaeterdeet terse =e eee ee eee eee e een eereeeee 39 Probably from Alum Bluff; the upper part of the posterior margin is slightly broken. 5. Arca staminata Dall; Oligocene of the lower bed at Alum Bluff, Florida; interior of a right valve. 6. Arca staminata Dall; Oligocene of Bailey’s Ferry, Florida; exterior of a young ‘ right valve. Ghd AERO AAIA ASE eon prane coe nba AoD ON noHdedapc ogo dadabcEndananIaoGenndonbosh dosbonabnghaaptocmoct 39 Miocene of Choptank River, Maryland; an unusual form, figured to show the variation of this species. 8. Arca staminea Say; Miocene of Choptank River, Maryland; valve with grooved ribs. 9. Arca staminea Say; Miocene of Choptank River, Maryland; common form. 10. Interior of the same. t1. Arca staminea Say; Miocene of Governor’s Run, Maryland; short, high form. 12. Interior of the same. 13. Arca staminea Say; Miocene of Choptank River, Maryland; short, high form. The umbo is angular and pointed instead of roundly inflated like the preceding. 14., Arca Zdonea Conrad). icisd doiesinciccsjusewei esoue sagierisoeneaeeee eas seeoese eae eee ee eee ee 41 Miocene of St. Mary’s River, Maryland. This is the form abundant at St. Mary’s River. 15. Interior of the same. 16. Arca idonea Conrad; Miocene of the upper bed at Alum Bluff, Florida. This is not very close to A. zdonea from Maryland. 17. Arca tdonea Conrad; Miocene of the upper bed at Alum Bluff, Florida; an extreme variation. Li, PLATE id VOLUM]I a a ie 4 va 22 PAL, : Det “i 86 Ror a é y ; - FIGURE 1. Arca santarosana Dall.........ctecereeeee a rheenaehed fos Ras abate Oligocene of Oak Grove, Florida. The eshte ribs are obscured by Ay mination. 3 & ky von 2. Interior of the same. , 3. Arca santarosana Dall; Oligocene of Oak Grove, Florida: right valve. 43, | Arca staminata: Dall wn scesa-chhestass as chaee Oe aera casa Probably from Alum Bluff; the upper part of the posterior ; broken. : toe = 5. Arca staminata Dall; “Oli€ocene of the lower aah at Alum Bluf, Florid es i aright valve. . sigs a) 5. Arca staminata Dall; a of Bailey’s Ferry, Fidsida; sie right valve. hte a.) Meet: xtamtines Siy.ty, sess cccsecendes st 38 Rae es de igeoeaee . Miocene of Choptank River, Maryland; an unusual form, figured tos variation of this species. } 8. Arca staminea Say; Miocene of Choptank River, Maryland; valve with ribs. : . 9. Arca staminea Say; Miocene of Ghatak River, pe rc common form, ne 10. Interior of the same. mall ft. Arca staminea Say; Miocene of Governor's Run, Maryland: short, high om . 12. Interior of the same. 15s 13. Arca staminea Say; Miocene 2 _Choptank Rives Maryland; short, high ate me umbo is angular and pointed instead of roundly inflated like the preceding. — en 14. Arca idonea Conrad...... ABE Sawer asvras earn acetate a eetemeate pane ee Remi cee cee shi eRe at 4i a4 Miocene of St. Mary’s River, Maryland. This is the form abundant at St. “S Mary’s River. : rs. Interior of the same. — 3 a5 : 16. Arca idonca Conrad; Miocene of the upper bed at Alum Bluff, Florida. This ag a. not very close to 4. zdonca from Maryland. 2 ne - 17. Arca idonea Conrad; Miocene of the upper bed at Alum Bluff, Florida; an extreme vatiafion. a IX PLATE L; GRAPHICA ANERICANA VOLUME FEON'T( PAL St * ae ° : 5 EN at arr # Pp haey al + pend L —f * - Lo ee” f “ eo iat Tt { . plot u = ate ea _ i etry oe - ey , : hy be . ‘ , iF, Sy - 7 = . to tecteciese z , - ‘ j - ’ . - “4 i * . - - i i, “ei ‘ ~ - . 5 “ ~ ihe oi a ‘ ‘- < ’ 88 PALAEONTOGRAPHICA AMERICANA 88 PLATE X FIGURE PAGE Tey AVGH CATOIMENSES WV AQTICI tenes els sso rice acts ser sane setistlstettettcts te ses eet ee ene eee 42 “Miocene of North Carolina; 56 mm.’’; after Dall. 2. Arca carolinensis Wagner; Miocene of North Carolina. 3. Arca callicestosa Wall .cnecrse-mocemoen ese neiseie cei cis(eciaicWel elelgeiee eect eee eee eee se sera 43 Miocene of North Carolina. 4. Interior of the same. 5. Arca callicestosa Dall; Miocene of North Carolina; exterior of a right valve showing the smoother ribs behind the middle. (Sa AI aPC LED ISTE ae genqacnoBS neo eonbO bbe ood soaHp ob sossobudod Add aaa HnosobsaS Has aSwaSSHASAos shasuons ITA 44 After Say. 7. Arca arata Say; “Interior of right valve. St. Mary’s River’’; after Glenn. 8. .Arca arata Say; ‘‘Exterior of left valve. Same locality’’; after Glenn. Q, Area) wprocera® COmrardy rem creme ler ere cle rn teler cio eiee tye elelee sel ele nse ele eles org eae een eee 44 Miocene of South Carolina. 10. Interior of the same. : 11. Arca improcera Conrad; Miocene of North Carolina. 12. Interior of the same. 13. Arca improcera Conrad; Miocene of Magnolia, North Carolina. 14. -4rca improcera Conrad; Miocene of Magnolia, North Carolina; a valve with a shorter hinge. 15. Arca improcera Conrad; Miocene of Magnolia, North Carolina; a valve with flat, rather smooth ribs. 16. Arca improcera Conrad; Miocene of Magnolia, North Carolina; a valve with nodu- lous anterior ribs and smooth central ribs. : 17. Arca buccula Conrad .-cnndeceseenscceneesetees= suse cce\teeat nese eaniecst) snide ca=e serene ees 45 Miocene of Magnolia, North Carolina. 18. Umbonal view of the same, figured to show the convexity of 4. buccula. 19. Arca plicatura Conrads.., ROL ee fter Conrad. ; Arca subsinuata Conrad, _ Pliocene of the Croatan beds of Nore Carolina. PALZZONTOGRAPHICA AMERICANA VOEUME) Ts, PVATE, Xx - oe eae ) ee Po Se y j ‘ ‘. 3 = .. qh bs ' wy P ; : flea ‘ a ix peut f ‘ -\ a ars : re spmewves’ YJ - eatin’ baat 7 ty vk vii A) gg’ 7 =" 4 A fe eae se ey - 7 — i : ; ? % e Lr) ae a |) ae Dikteiic 5 5 A. A ‘ 7 a) . i j - ¢ . . iD ve vy a an, ay ty " ‘ (fe) PALAEONTOGRAPHICA AMERICANA go PLATE XI = FIGURE PAGE cr. Arca campyla Wall...c.cscconcsassnrssnasase serdsese onda dcnsacsteseae sea - tees ee ae ee eee 47 “‘Caloosahatchie beds; side view; lon. 37 mm.’’; after Dall. 2. Arca campyla Dall; ‘‘Umbonal view, showing tortuosity of the valves; lon. 37 mm.’’; after Dall. 3: Arca campyla Dall, var. aevetea Dall; ‘‘Pliocene of Shell Creek, Florida; 34 mm.’’; after Dall. Ae APCD TFANSUETSALSAY occa ccs snece Wee dae soem lelseenesesenece- sea cote eee ae ERE EEE EEE Eee 47 Recent from Florida; showing the nodulous anterior and flat central ribs of the right valve, and the extension of the left valve beyond the right. 5. Left valve of the same, showing the rounded, nodulous ribs. 6. Interior of the left valve. one 9. Arca triphera Dall sccne ge sive accsen ss ecsancolast scan setestoedeess aeaee eee tee oe ae eRe eee 48 “Caloosahatchie Pliocene; 18 mm.’’; after Dall. 8. Arca halidonata Da iis: iotsc ce. owcen sree secise es aseae ieee ae eee Eee eee Eee 49 “Oligocene of Bowden, Jamaica; 56 mm.”’; after Dall. 0. Arca Consobrvina. SOWELDY i. :.s2 5.00 secissoseee Sa toes soasoaceseene sce ac reece eee ce aereeene CR eeRrt aes 49 After Sowerby. 10. Arca consobrina Sowerby; after Sowerby. Ib. Arca; inequilateralts (Guppy sc0xs-sct -'nvctiosevstinacesiseces eeceeesee se est hetae cere eee eee 50 After Guppy. 12. Arca inequilateralis Guppy; after Guppy. 13. Arca actinaphoras Dall). iicessn asascensnee -cneccincseesod steele eceecer eee ee eee eRe eee 50 “Oligocene of Monkey Hill, Panama Railway; 46 mm.’’; after Dall. 14... Axed donactia Wall riss = gsadepoas sete scise)-tece ne cteaceee tater ne ees eeee ces aeee ee eee eee 50 “Oligocene of Bowden, Jamaica; 6.5 mm.’’; after Dall. 1g. - Arca’ Deshayest Danley ...issexcscaseceaseccenseeceseseneneactencdeecterersceeecesenasseseeeees 50 Recent from Guadeloupe. The peripheral part has been modified in the en- graving process but the outline is approximately correct. 16. Umbonal view of the same. 17. Arca Deshayesti Hanley; young; recent from Jamaica. Figured to show the pos- terior auriculation of the young. 18. Umbonal view of the same. 19. Arca aurtculata’ Vamarck....2c2c.<. cc pehe nae ronsre soee soa eae sene Soe ee REE EE 50 Recent from Florida. The degree of auriculation varies. It is greater in the young. P\LZONTOGRAPHICA AMERICANA VOLUME I PLATE XI] Bea Mi Ae o wr ¢ penn ag. AW a 4 TETAS Ss UH Kos sey Ra 4uWana yao oes ai HUA SS ALLAN A ASS PPGSAL TESS VL kde Htrveres* PALAEONTOGRAPHICA AMERICANA go E S 7 ; : r PLATE XI fi 3 FIQURE t 1. , Avca, Cambypla Dalle. iccsecs20a,toss lactasetenactageneties ienea seseeneeeseeseneeasae seeennaee sss se. ae 18. 19. ‘‘Caloosahatchie beds; side view; lon. 37 mm.’’; after Dall. ane Ri 4 Dall; ‘‘Umbonal view, _ Showing tortuosity ‘of the Eee Jon. 37° a ; after Dall. tet Pay ay aes ey te ‘Dall, var. aevetea Dall; ‘‘Pliocene of Shell Creek, Florida; 34 mm." Gfter Dall. Ps Arca: transversa SAY. ics Ww NaN nn gs 0 Seren ale ep ee ong cree gree Miocene of North Carolina. The posterior margin is broken. Arca glisea Dall; “Miocene of Virginia; 56 mm.’’; after Dall. Arca arestaDalls....: 2.30 ios ope Boakan See Se ee eee Doreen ee Per re hes Miocene of the upper bed at Alum Bluff, Florida. : Umbonal view of the same. Arca aresta Dall;. Miocene of Alum Bluff, Florida; interior of a younger valve, with less attenuated posterior end. Avét campsi Dall. sic dipis cscabace 802 tua trex’ poennn to Seeks Meobaaey cea scciapdser ss ebeecoenall 54 Miocene of Alum Bluff, Florida; figured to show the form of the young. Il o1 SI >AU Me PLATE VOLUME I., REE NNN ee YP fs 94 PALAEONTOGRAPHICA AMERICANA 94 PLATE XIII FIGURE PAGE 1. Arca Campsa Wall... ...ccccceeseccneeesmentersonsens cnceissesi ssesen. Interior of the same, showing the thickening of the anterior end of the hinge. 3. Arca campsa Dall; Miocene of the uppet bed at Alum Bluff,eFlorida; umbonal view 10. II. PALAKONTOGRAPHICA AMERICANA of an adult specimen, broken posteriorly. Arca rustida Tuomey and Holmes.........cccccccqeecesecsereceeceeeeeasereees geasvidte vee aH Pliocene of Shell Creek, Florida; exterior of a young left valve. Arca rustica Tiomey and Holmes; Elec. of Shell Creek, Florida; interior of a young left valve. Arca catasarca Dall......... ...+.. POM PR RN te Drier ep y fart RE el aur 56 “Pliocene of Alligator Creek, Paige 55 mm.’’; after Dall. Arca initiator Dall.............04.- Nis swidie scien lle whleg.s abies ase wre abate ae el nie Sata Was Stee a 56 Oligocene of Sour Lake, Texas; 2.7; interior of a large left valve. Umbonal view of the same. Near the center of the ligament area on this specimen there is an incipient second v-shaped groove. It was lost in the engraving. Arca initiator Dall; Oligocene of Sour Lake, Texas; X 2.7; exterior of a left valve. Arca scaldris Conrad. :si.. ciscicon occas, obeadeniile secsaaeseneoumane! olan hwenensasianesaeGigeaenee 57 “Exterior of left valve, and hinge and teeth of right baa ; after Tuomey and Holmes. Ayca scalaris Conrad; Miocene of North Carolina; exterior of a ere right valve, showing the interstitial ribs. - < 84rca scalarina Heilprin; Pliocene of Shell Creek, Florida; interior of a left valve lent by the U. S. National Museum. The teeth are worn. This figure shows the cardinal area characteristic of-Cunearca. ) Arce Blacials Gray si ieies } OG Oe fea eS a ie Pis PREFATORY REMARKS During the months of August and September of the years 1920 and 1921 the senior author had the opportunity to visit the island of Trinidad under the auspices of the Trinidad Petroleum Development Company. Sundry paleontological collections, main- ly of Miocene age, had already been received at Cornell from the Island some months before these visits were made. During the present year, 1922, other collections from various horizons have been received. ‘The classification and description of all this ma- terial is proceeding as rapidly as time will permit and it is hoped that the greater part will be ready for publication during the coming year. The present paper takes up one small group of mollusks represented on the Island, the Rudistids, which appear so different from anything already published that their de- piction with such detail as is now possible seems eminently desirable. The occurrence of this type of molluscan life on the Island seems never to have been suspected, at least not reported, till our first visit (1920) referred to above. Guppy had noted the occurrence of Cretaceous fossils at Point 4 Pierre but seems not to have surmised the existence of Rudistid forms; his reference to large Naticas suggests that he may have seen the upper valves of some Caprinoid form and supposed them to be large univalves. Etheridge says in ‘‘Appendix J’’ of Wall and Sawkins Report of 1860: ‘The compact limestones of the Older Parian group, both at Point 4 Pierre and in the interior, contain numerous regular masses of crystalline carbonate of lime, which has evidently resulted from a charge of organic remains, but the form is usually so far obliterated that even the genus cannot be determined.”’ The Rudistid character of many of the fossil remains at the so-called Stack Rock at Point a Pierre cannot be doubted, asthe illustrations on Plates roand 11 will show. But by far the best specimens we have so far discovered come from the banks and bed of a small stream west of the Plum Road, about two miles north-east of Mt. Harris, in the eastern part of the Island. Here the calcareous material in which the fossils are im- bedded is less crystalline and hence the forms of the various species represented can be quite easily determined. Cross-sections with polished surfaces show the canal systems to great advantage as may be seen by consulting Plate 4. é Trinidad is an island mass that has been the site of extensive earth movements; folds, faults and overthrusts may be expected almost anywhere. Question has already arisen as to the extent and continuity of these calcareous, Cretaceous outcroppings, some believing them simply great boulder-like masses floated in Miocene deposits, others that quite probably they are still in connection with extensive Cretaceous formations below. 6 PALAONTOGRAPHICA AMERICANA 124 The horizon they represent in the Cretaceous is probably about Cenomanian though the accompanying fossils are generally too indefinite to make the determination certain. The review of the Rudistid literature, more specifically that of the canalled Caprin- ide, by the junior author, brings to light certain noteworthy facts: a. Much has been written on this type of life; comparatively little in English, mostly in French. b. Generic names have been applied often to forms differing but slightly, yet none seem applicable to the most abundant and best preserved specimens from Trinidad. The summation of characteristics ascribed to known genera may well serve as an in- troduction to the description of the Trinidad forms. + + + We are indebted to the Trinidad Petroleum Development Company for the privilege of publishing these interesting details, and especially to Mr. G. A. Waring, in charge of geological work on the Island for his great assistance in securing large shipments of organic remains. Paleontological Laboratory, Cornell University, Lihaca Ne Ye September 22, 1922 ioe RU DISEIDS OF PRINT DAD G. D. Harris AND FLoyp Hopson GENERAL CHARACTERISTICS AND DISTRIBUTION OF RUDISTIDS Rudistids are aberrant, sessile Pelecypods which may be attached by either valve; the valves may be twisted, capuloid, or straight and conical; the test may be replete with cavities in one or both valves; the canals may be true cavities found in the inner layers of the test (Caprinoid forms) or highly developed prismatic cellular structure in the outer layers of the test (asin Hippurites). The position of the ligament varies, being inter- nal, marginal, external, or even absent. The form, kind, and relative disposition of the cardinal teeth vary. This type of life originated in the Jurassic and reached its maximum development and expansion during the Cretaceous period. Thick beds were often formed from the remains of these sessile gregareous animals, which thrived in large colonies in clear, warm, shallow seas. Douvillé,* especially, has emphasized the almost identical geo- graphic distribution of this type of molluscan life with certain large foraminferal genera. In general it is his Mésogée, the Tethys of others, extending from the Mediterranean- East Indian region of the Old World and including the West Indies and Mexican region of the New. Certain Ammonites, Belemnites and Echini are also limited to this zone. POSITION OF RUDISTIDS IN THE ANIMAL KINGDOM The strange appearance made by these fossils in their usual state of preservation caused them formerly to be referred by different authors to widely different classes in the Animal Kingdom. Woodward sums up these references as follows: (Manual of Mollusca, p. 441. 1871.) 1. Buch regarded them as Corals. 2. Desmoulins, as a combination of the Tunicary and Sessile Cerripede. 3. Dr. Carpenter asa group intermediate between the Conchifera and Cerripeda. 4. Prof. Steenstrup, of Copenhagen, as Annelids. 5. Mr.D. Sharp refers Wzppurites to the Balani; Caprinella to the Chamacez. 6. LaPayrouse considered the Hippurites Orthocerata, the Radiolites, Ostracea. 7. Goldfussand D’Orbigny place them both with the Brachiopoda. g. Lamarck and Rang, between the Brachiopoda and Ostracee. g. Cuvier and Owen, with the Lamellibranchiate bivalves. to. Deshayes in the same group with the 4theria. 11. Quenstedt, between the Chamacee and Cardiacee. * B. G. s! Fr., (3), vol. 28, pp. 222-226, Igoo, 8 PALA ONTOGRAPHICA AMERICANA 126 Douvillé* remarks in 1886 that: Les remarquables traveaux de Woodward et de M. Bayle ont démontré d’ une maniére incon- testable que les Rudistes sont des Mollusques lamellibranches qui doivent étre places dans le voisinage des Chamacés. Cette opinion est universellement adoptée aujourd’hui CLC ELC. In 1912 the same author concludesy: On voit done que les Chamidés ne sont pas proches parents des Rudistes comme on le dit habituellement, et comme je l’avais cru moi-méme au début de mes recherches. Sans doute, ils dérivent des Hétérodontes par le méme processus de fixation direct, mais il semble qu’ils dérivent de types différents et a des époques différentes, les Rudistes des Cardiides a la base du Jurassique supérieur, et les Chamides des Lucinides pendant le Crétacé supérieur. CLASSIFICATION The term Rudistes was used by Lamarck in his Animaux sans Vertebres to include six genera which he supposed belonged between Ostrea and the Brachiopodes, namely: Spherulites, Radiolites, Calceola, Birostrites, Discina and Crania. But in more recent usage it may include a great series of forms ranging through Diceras, Reguienia, Mono- pleura, Caprina, Radiolites, Hippurites and even Chama. As so understood the first rational classification was made by Munier-Chalmas} who divided the then known spe- cies into the following seven families, embracing 23 or 24 genera: Chamide, Monopleur- ida, Balyeide, Caprinide, Heterocaprinide and Radzolites. Since this classification was proposed, many modifications have been suggested and many new genera described. Stress in classification is now generally laid on the fact that some forms may be considered ‘‘normal’’, attached by the left valve, or ‘‘inverse’’, attached by the right valve. Some early Jurassic Diceras from which all later forms of Rudistids were doubtless derived, were indifferent as to mode of attachment, but in late Jurassic times they were all ‘‘normal’’, attached by the left valveS$. Both normal and in- {B. G. S. Fr. (4) vol. 12, 1913, p. 454. {Journ. de Conchyl., (3), vol. 21, 1873, pp. 71-75. ¢ZDouvillé, B. G. S. Fr. (3), vol. 15, 1887, p. 758. 127 PALMONTOGRAPHICA AMERICANA 9 Note:—It was formerly supposed that in all Chama-like forms the attached valve, whether right or left, had the same dentition; the same remark applies to the free valve. Hence the Attached (lower), left valve N Normal Rudistid formula: ee Free (upper), right valve BoB Attached (lower), right valve N and the /nverse-: a ee Free (upper), left valve B’ B The letters n, b and b’ were used for corresponding tooth sockets. See plate 5. According to Douvillé* the accepted notation is now: All 36 For normal — for inverse Al, 36 AIL, PII i. e.,*‘ la charniére des formes inverses dérive directement de celle des formes normales par le dévelop- pement d’un élément nouveau et la disparition d’un autre élément.”’ The /nverse forms deploy in two great series throughout the Cretaceous. One has been called the Gyropleurides, the other, AJonopleurides +. ‘These two series are differ- entiated from more primitive forms by the gradual development in the upper valve of an apophysis or muscle-bearing plate, bearing the posterior muscle on its external sur- face Monopleurides on its internal surface (Gyropleurides). Paquier (doc. cif.) distinguishes the A/onopleura from the Gyropleura ‘‘phylum’’ by its lack of a posterior myophore plate, so called, in the lower valve. The muscular impression is represented by a thickening more or less defined on the inner shell layer. The relationship of several of the common genera belonging to these series to- gether with our new forms (in Italics) are roughly expressed in the following table: Jurassic Cretaceous Gyropleurides Caprotina Caprina Plagioptychus Hippurites Horiopleura Pachytraga Praecaprina Gyropleura Spheerucaprina Valletia Schiosia Coalcomana Inverse Amphitriscelus Kipia Monopleurides Monopleura Agria Polyconites Ichthyosarcolites Radiolites Diceras — — —--—— ~-- = Heterodiceras Requienia Matheronia Toucasia Normal Apricardia Bayleia * Sur Lappareil cardinal des Chama; B. G. S. Fr., CR. somm., vol. 15, 1915, p. 75. t See Paquier, Mem. Soc. geol. de Fr., vol. 13, 1905, p. 50; also Douvillé B. G.S. Fr., vol. 28, 1900, p. 210, Io PALHONTOGRAPHICA AMERICANA 128 In studying over the Trinidad material we have found no specimens showing clearly well defined dentition. All except the Plum Road material is in a very unsatis- factory state of preservation. Here, however cross-sections show the shape and_ posi- tions of the internal cavities and canals to perfection. Naturally, our diagnoses of new forms and determination of relationships with those already described must be based largely on cross-sections. Accordingly, a synoptical key has been prepared showing the main differences and resemblances of our new genera to those already described in so far as arrangement of internal cavities and canals are concerned. It may be stated at the outset that it is only the Rudistids having well defined canals, and more particularly those having canals in both valves, with which we are here concerned. Asa rule, the relationship of these American to European forms seems decidedly remote. KEY TO GENERA I. CANALS IN ONE VALVE ONLY A. Canals in the upper valve. Lower valve straight and conical; accessory cavity n’ and socket n united. rt. Canals polygonal and radial: polygonal canals on the inside, radial and bifurcating outside; wanting dorsally. Ligament external ...... Fackcss eas dodncsasees ssestsiaceecesnaairasionaenne Mitrocaprina Boehm (Palzeontogr. vol. 41, 1895, p. 102.) 2. Canals pyriform, especially the inner series, bifurcating exteriorly; lacking dorsally. Ligament marginal (external) .................:....0---- dele esine eae aiciee sities siastaere slo namslswisseble nlejsetsiaeries Plagioptychus Matheron (Cat. Méth., 1842, p. 144; B. G.S. Fr., vol.16, 1888, p. 713, p. 718 fig. 5.) Herewith refigured as pl. 5, fig. 9. B. Canals in the lower valve. Upper valve without accessory cavity n’. 1. Large coiled lower valve with a partition, canals mostly circular; upper valve with myophore polygonal canals. Muscles attached on exterior sides of apophyses in upper valve...... Tchthvosarcolites Desmarest. (See Douvillé, B. G. S. Fr., vol. 15, 1887, p. 791). 2. lower valve without a partition. No ligament. Form of shell and myo- cardinal arrangement much like Monopleura. Very small polygonal canals around the whole circumference. Canals divided by transverse septa as in Coralliochama ............ Rousselia Douvillé (B. G. S. Fr., vol, 26; 1898, Pp: 151, text dig. 19). 129 PAL ASONTOGRAPHICA AMERICANA 11 Il. CANALS IN BOTH VALVES A. Interior of upper valve bipartite (Gand n+n’'), lower valve without a par- tition. 1. Cavity n’ large, separated from small n. a. Bothvalves with double or treble series of polygonal canals through- Outipernipheny.sascseseeer ee Caprinula a’ Orbigny (Paleont. Fran., 1847. See especially Douv. in B. G. S. Fr., vol. 15, 1887, p. 784. See also pl. 5, figs. 5 and 6 of this memoir. b. Upper valve with polygonal canals dorsally; radial ventrally. Low- er valve with few canals, none ventrally ..................:ceeseceeeeeees Seu ddietencladse coesebemeer tena Caprina ad’ Orbigny (d’ Orb. pére, 1822. See Douv., B. G. S. Fr.,vol. 15, 1887, p. 781, pls. 29, 30, 31). 2. Cavities n’ and n not separated. a. Canals of single series; in upper valve, simple, polygonal or roundish, generally outside of myophores only. a. Canals well developed in upper valve, few in lower valve. Greatest diameter of shell from anterior to posterior ......... BPR cetera meat mecesneeie Precaprina Paquier (Mem. G. S. Fr., vol. 13, fase: 4 1905, Pp: 72, pls: 8) 9, 10))) Seevalsomplers: figs. 3 and 4 and pl. 6, figs.r and 2 of this memoir. 6. Canals of regular pattern, mainly found outside of anterior myo- phore. tr. Upper valve high capulid; lower long, curved. Shell Short trom antenonr tO) pOStenOor a... eee seseaceeeee nee detlsyisteisnlghie sskis eoarearnsieehn Pachytraga Paquier, 1900 ; (see especially Mem. G. S. Fr., vol. 13, fase. 4, 1905, p. 61, pls. 7-10). 2. Upper valve Venericardia-like, when decorticated ; lower valve short-conical... A7pza, n. gen., pl. 7. b. Canals of double or triple series in upper valve. a. Canals not horizontally divided, i. e. not tabulate. 1. Canals largest and best developed anteriorly and posteriorly, sometimes poorly developed ventrally....................... pane SbboSaeOEBcE cman Offnerta Paquier (Mem. G.S. Fr., vol. WGutAasc= 41005, P:S2, pls. Il, 12). 2. Canals best developed dorsally, filling 34ths the whole 12 PALAONTOGRAPHICA AMERICANA 130 shellcavityen eN Omlic aime titmewepcrseocrcrcneincdecee ter teases Sad norAneno anos eaesaToonoG Polyptchus Douville (B. G. S. Fr., vol. 4, 1904, p. 523 and text figs. 1 and 2). 3. With only the one large sinus or cavity (omp) in the low- er valVerscsencr cnr Spherucaprina Gemmellaro (Att. dell’ Accad, Gioenia di Scienze Natur. di Catania, 2d. ser. Voll 20) L865, 9p) 2th a plea). 6. Canals tabulate, small ...... Coralliochama White ( Bull. U. S. G'S. No} 225 1885) png) pls:ei-4)e B. JLnterior of both valves bi- or tripartite (G, n+n', and often b greatly ex- tended). 1.. Both valves tripartite, one series of canals, wanting ventrally ............ setesite.s peetseeeceeseeee A mphitriscelus, n. gen. (see pls. 1-4 of this memoir ). 2. Lower valve the larger, tripartite ; whole periphery of shell with com- pound, pyriform canal system. Coalcomana, n. gen. (see pl. 6, figs. 4-7 of this memoir). 3. Upper valve the larger, tripartite; dorsally with a few large cavities; radi- al canals ventrally developed ; lower valve small, capulid, not well déseribed! Aissescas, gesercwoessent Schiosia Boehm (Ber. d. Naturf. Gesell. zu Freiburg, I. B., 1892, pp. 134-148, pls. 7 and 8). DESCRIPTION OF SPECIES Amphitriseelus, n. gen. Etymology : amphi, both - fzs, thrice - ce/us, hollow Amphitrisceelus waringi, n. sp., Plates 1-4 Generic characterization.— Shell of form and dimensions approximately as shown in the accompanying illustrations; both valves curved, but not in the same plane; sur- face marked by very fine lines of growth; substance of the shell, including septa within, very thin; canals in a single series, of polygonal type, absent ventrally; both valves with two large ‘‘ ior subdivision. accessory’’ cavities, hence showing in cross-section a tripartite inter- Specific characterization.— Valves usually ranging in length from 15 to 120 mm. and in diameter, at the commissure, from 10 to 35 mm.; cross-section nearly circular, slightly longer from ligament pit to ventral margin than anterio-posteriorly; ligamental groove not deeply sunken, extends from commissure to tip of either valve; upper valve usually shorter and more incurved or coiled than the lower; concentric lines of growth : ‘ ee) 131 RuDISsTIDS OF TRINIDAD 13 times showing slight irregularities in frequency, or stages of growth; often just above or below the commissure, perhaps Io mm., the shell suddenly contracts in diameter to the extent of I or2 mm. ; beaks more or less prosogyrate; canals quadrangular; largest anteriorly and posteriorly, smaller above, wanting ventrally; body cavity, i, more or less pentagonal with one side the (ventral) much the longest, delimited exteriorly by two longitudinal faint grooves, of which the posterior is the more pronounced; posterior cavity, 2, more or less scoop-shaped in cross-section with handle somewhat depressed; anterior cavity, 3, smaller, quadrangular, or becoming more or less triangular to roundish; in distal, abandoned portions of the shell all walls are thickened by calcareous deposits* leaving clearly visible simply a small circular body cavity; near the commissure there isa thickening of some of the internal septa evidently caused by dentition develop- ment, though the exact shape and size of the teeth cannot be made out from the ma- terial in hand; muscular attachments not clearly shown. Remarks.— Cross-section made just above and below the commissure, see pl. 5, figs. 1 and 2, show besides some irrelevant matter what seem to be the sections of the teeth of the lower and upper valves. These sections when taken in connection with others would indicate that the teeth of either valve extend but a short distance into the other. Yet specimens when closed are broken apart at the commissure with almost as much difficulty as at any cther place. This may be due to secondary crystallization. Attachment or fixation is by the tip of the lower, right valve, which is generally rather sharply curved and flattened in the plane of the general curvature of the valve. The amount of torsion and the rate of expansion in growth and the general shape as well as size of the lower valve show many and marked variations. The upper valve shows perhaps still greater variation in general manner of growth than does the lower. It may be nearly as long as the lower or may be little more than capulid. The upper valve has the appearance of curving off in a plane nearly at right angles to the plane of curvature of the lower valve (See pl. 3, fig. 2). The commissure, especially in young specimens is not normal to the axis of the shell, but is very oblique, being therefore elongate-elliptical in outline. The most remarkable feature of this genus is the tripartite subdivision and almost complete identity of interior characteristics of both valves when sectioned anywhere except very close to the commissure. We know of no other genus heretofore described showing constantly in both valves two large accessory cavities besides the body cavity. The thinness of the various partition walls, especially where one would look for myo- “s Compare thickness of partition walls in pl. 4, fig. 7, with those of the top of same specimen shown as fig. 6. 14 PALAONTOGRAPHICA AMERICANA 132 phore attachments is noteworthy. Thickening locally may occur, but in most instances seems due to secondary replacement. Schiosia as originally characterized by Boehm (Ber. Naturf. Gesell. zu Freiburg i. B. 1892, p. 134) has a heavy shell, with a very small lower and a very large upper valve. The lower valve was too poorly preserved to admit of accurate description. The upper is shown herewith as pl. 6, fig. 3. In a subsequent publication (Palaeonto- graphica, vol. 41, 1895, p. 129) this author in describing a species, foro /uliensis, remarks; ‘The lower valve which belongs to the species just described is not definitely determined. Con- sequently, therefore the generic determination is uncertain. One may be dealing with a Caprina. For the present I place this form in Sckiosta, because here as with the type of the genus already referred to, over #za a large accessory pit is developed. Similar pits are found in Caprvinula (B. G.S. Fr., XVI, 1888, pl. 23, fig. 6a.) and also in Sphe@rucaprina striata already described. Yet in these there are developed besides the radial, also polygonal mantle marginal canals. In Caprina, as in Schiosia which has exclusively mantle margin radial canals, the accessory pit over ma so far as I am aware is lacking; or it is at least, as represented in Douvillé’s text figure (B. G. S. Fr., vol. XVI, 1888, p. 703, text fig. 3) subdivided by a row of septa. Still it is not proven that these septa are not pres- ent in Sch7osia and are simply not preserved in our specimens, The pit he refers to in this quotation is clearly shown on pl. 11, fig. 2 of this volume of the Palzeontographica and seems more analogous to the third accessory cavity of Amphitriscelus than does the broad cavity shown in the type of Sc/vosta herewith copied as fig. 3 on plate 6. The Schiosia ramosa (Boehm) Douvillé from the Caprina limestone of Coalcoma Mexico has been cross-sectioned and described in detail by Douvillé (B. G. S. Fr., vol. 28, 1900, p. 207). It is a curious and interesting form. But we are at alossto know why it has been considered referable to Schiosta. In this genus, as originally described by Boehm the upper valve is very large, the lower very small; here Douvillé says the upper js capulid and the lower often very much elongated. ‘The marginal canals in Schzosza are simply radial, but in the Mexican form, pyriform and bifurcating; in Schzosta, in the upper valve there is a great pit over ma according to Boehm, but in the Mexican form (see pl. 6, figs. 4-7) no such pit is shown. However, in the lower valve, not well described by Boehm but shown in the Mexican form (pl. 6, figs. 6-7) as a pit for tooth B’, such an anterior cavity exists. The arrangement of the body and accessory cavities of the lower valve of this form is strikingly like that of Amphztriscelus, but the peripheral canals are totally different. This peculiar form, first regarded by Boehm as a Carina, later by Douvillé as Schiosia may well receive a new generic designation, and Coa/comana is here proposed. 133 RUDISTIDS OF TRINIDAD 15 In the simplicity of structure of the single polygonal series of canals with a hiatus ven- trally, there seems to be a similarity between the upper valve of Precaprina varians and Am. waring?. But the former is wholly lacking in a great accessory cavity over “‘ma’’ as shown in Paquier’s works. (See pl. 5, fig. 3, of the present memoir). The large ‘‘b’ ’’ and the ‘‘o’’ over ‘‘ma’’ in the lower valve show that there is an inherent tendency in this line of Rudistid development to produce large cavities here. Posterior marginal canals seem lacking, still, the great cavity ‘‘omp’’ is doubtless a primitive representative of the same. Inan allied genus Pachytraga (paradoxa) as shown by Paquier there is however, a fairly regular series of canals outside of ‘‘ma’’. But the systematizing and standardizing of the tripartite interior with the clearly defined uniser- ial system of canals as shown in Amphitriscelus very probably took place at a somewhat later date than that represented by Paquier’s genara, perhaps as late as the Cenomanian. The tripartition in the lower valve of Coa/comana accompanied by the complete canal- ization of the periphery suggest perhaps an even more advanced stage of specialization than that shown by Amphitriscelus. Douvillé suggests that this form (his ‘‘Schzosza vamosa’’) is most likely of Cenomanian age (B. G. S. Fr., vol. 28, 1900, p. 217). Locality and Horizon— Practically all the material herein discussed is from an out- crop of yellowish gray impure limestone in the bed of a small stream 1 mile above where it crosses the Plum Road just south of the 5% mile post. Fragmentary mater- ial has been found ina stream a short distance south of the 5 mile post. -It seems most likely that these fossils represent a Cenomanian horizon, though they may well be as low as the Aptian. Kipia. New Genus Kipia trinitaria, n. sp. Plate 7 Generic Characterization,— Shell small with short, conical lower valve and low capulid upper valve; regular series of canals simple so far as known, developed only anteriorly and ventrally; substance of shell thin especially posteriorly; body cavity oc- cupying practically the whole of the interior of the shell. Specific Characterization— Polygonal canals beginning small anterior to the umbo in the upper valve (see pl. 7, fig. 3,) increasing in size to the anterior ventral margin; decreasing posteriorly and becoming of minute size and vanishing at the posterior ven- tral margin; from the beak anteriorly the shell matter was seemingly thick, but with at least some cavities; one for the myophore of the opposite valve (see fig. 6 for a rough representation of a section just above the commissure); lower valve angular in cross- 16 PALAONTOGRAPHICA AMERICANA 134 section, more or less as shown within the heavy line, fig. 6; canals more numerous and smaller than in the upper valve; well developed anteriorly and ventrally but lacking posteriorly; spaces between body cavity and anterior marginal canal series with cavities whose size and dimensions have not yet been determined; anterior to ‘‘ma’’ (see fig. 6 ) a deep, narrow pit allows the filling matter of the upper valve to extend downward in a very thin wall one-fourth way to the apex (See fig.1); attached to a valve of Amphitriscelus waringi along the straight side (fig. 6 opposite ‘‘L’’) from beak to near the commissure as indicated in fig. 1. Of this strange type we have found but one specimen and that is imperfect. We have naturally felt much hesitation in placing this on record as a new genus and spe- cies, yet it is mainly in the matter of the inner series of anterior canals that medifica- tions and improvements in the description above given can be made, a matter, how- ever, that cannot seriously modify the general make-up of our diagnosis. Fragments indicate that there are still other strange types of Rudistids to be found in this eastern ‘Trinidad locality. Locality and horizon, — Found in connection with Amphttriscelus waringi at the type locality for that species near the 514 mile post on the Plum Road in the eastern part of Trinidad. Genus Caprina, d’Orb. Caprina plumensis, n. sp. Pl. 8; 9, figs. 3, 4 Specific charactertzation.—Shell of moderate size; upper valve coiled in a loose spiral as shown in figs. 2 and 4, pl. 8; cross-section roughly ovate with ventral por- tion flattened, tending to be a little carinate just anterior to the basal terminus of the one, strong partition; exterior with fine growth lines, where not decorticated; shell wall thick, with traces of narrow quadrangular canals ventrally, becoming large an- teriorly and posteriorly, indefinitely and widely developed along the ligamental margin; anterior tooth (B’) generally represented by an open cavity in cross-sections, posterior (B) indicated by a thickening of the exterior wall, in some instances; lower valve as seen in fragments seems to be less coiled, smaller, with a few very large quadrangular canals posteriorly where the shell wall is thick, very small quadrangular canals anter- iorly, and with very irregular cavities in the ligamental region. The specimen from which fig. 2 was drawn was doubtless twice the length shown before it was broken to pieces in extracting the specimen from the matrix. Much better material must be secured and worked out before the generic position 125 RUDISTIDS OF TRINIDAD 17 of this species is well determined. Locality and horizon. In eastern Trinidad near the Plum Road, associated with Amphitriscelus. Comparatively scarce. Genus Precaprina Precaprina andersoni, n. sp. PAL Kole soles a Specific characterization.—Shell of moderate size (upper valve only known); beak closely incoiling on a plane with the anterior margin of the shell, giving the outline of the whole valve a pentagonal appearance with anterior side longest; ventrally the shell is slightly concave anteriorly but rather sharply carinate sub-centrally, with a trace of a second carination further towards the posterior; surface when uneroded covered with a fine spiral costation, especially well defined about the beak; canal system seemingly not far from that of Almmensts; partition in specimens studied apparently dissolved away. The shape and method of coiling of this valve suggest strongly Precaprina, yet the canals as faras can be made out are more continuous ventrally and less angular and cavernous anteriorly and posteriorly, than represented in illustrations of that genus. Locality and Horizon.—Found, very rarely, along with C. plumensts and Amphi- triscwlus, near the Plum Road, eastern Trinidad. Precaprina? pennyl. un. sp., Pls. 10, 11 Specific characterization. Shell of moderate size; upper valve rather closely coiled with apex nearly in the same plane as the anterior margin of the shell; outline of cross- section, oval, slightly flattened from ligament anteriorly and ventrally; a well defined partition present; quadrangular canals along the anterior and posterior margins with greatest dimension parallel to the shell margin; lower valve slightly curved or mildly ir- regularly twisted; without a partition; walls generally appearing very thick. The general appearance of these specimens is like that of Coralliochama or Pachy- traga. ‘The character of the canals along the ligamental margin cannot well be deter- mined with our specimens so broken and in such crystalline condition. So far, we have observed no canals ventrally. They are comparatively few anteriorly and posteriorly. Locality and Forizon.—The so-called Stack-Rock at Point a Pierre, Trinidad. The European affinities of these specimens would seem to point to a horizon at least equally as low as the Plum Road material. This remark has reference to the fossils in Stack-Rock and implies nothing as to the supposed transplanting of this rock subse- quently in beds of far higher horizon. Along this coast loose fossils have been found from time to time, which when studied in connection with other Stack-Rock material may give a more definite clue to the age of the Rudistid remains. 18 PaL#ONTOGRAPHICA AMERICANA 136 BIBLIOGRAPHY Almera: Etude stratigr. du Massif crét. du litt. de la prov, de Barcelone. B.S. G. Fr., (3), X XIII, p. 569, 1895. Réunion extraord. de la Soc. géol. A Barcelone. /dem, XXVI, p. 851, 1898. Bayle: Sur la structure des coquilles des Hippurites, et quelques remarques sur les Radiolites, B. S. G. Fr., (2), Vol. 12, pp. 772, 1855. Sur le Sphzerulites et Radiolites. /dem, Vol. XIII, pp. 71-85, 1855. (Gzves ref. to earlier authors.) Berry: Hippurites from South America. Pan-American Geologist, Vol. 37, pp. 272-274, 1922. (Hippurites). Blayac: Sur le dome de Sidi-Rgheiss (Prov. de Constantine). /dem, (3), XXV, p. 664, 1897. ( Toucasia). Boehm: Ein Beitrag zur Kenntniss der Kreide in den Venetianer Alpen. Berichten der Naturf. Gesells. zu Freiburg i. B., Bd. VI, Heft 4, pp. 134-148, 1892. (Schiosta, Caprina, Sphaerucaprina). Beitrige zur Kenntniss der Kreide in den Stidalpen. Palewontographica, Vol. XLI, pp. 99-143, 1894. (Caprinide—Good bibliography). Beitrag z. Gliederung der Kreide in Venetianer Alpen. Z. D. G. G., Vol. 51, p. 180, 1897. (/oujia). Zur Kenntniss der Gattung Jovta. /bid., p. 8; Jahrg. p. 592, 1898. (/ou/fia). Ueber Caprinindenkalke aus Mexico, /dem, Vol. 50, pp. 323-333, 1898. (Brblio- graphy). Choffat: Faciés Ammonitique et Faci¢s Récifal du Turonien Portugais, B.S. G. Fr., (3), p- 472, Vol. 25, 1897. (Sauvagesia, Toucasia, Biradiolites). Douvillé: Essai sur la Morphologie des Rudistes, /dem, (3), Vol.14. pp. 389-404, 1886. Sur quelques formes peu connues de la famille des Chamidés. /dem, (3), Vol. 15, pp. 756-802, 1887. Etudes sur les Caprinés. /dem, (3), Vol. 16, pp. 699-730, 1888. (Caprina, Caprinula, Plagioptychus). Rudistes du Crétacé inferieur des Pyrénées. /dem, (3), Vol. 17, p. 627, 188g. Etudes sur les Rudistes.—Ré€vision des principales éspeces d’Hippurites. Mem. No. 6, Mem. Soc. Géol. de France, Pal., Vol. 1, 1890; Vol. 2, 1892; Vol. 3, 1293; Vol. 4, 1894; Vol. 5, 1895. 137 RUDISTIDS OF TRINIDAD 19g Sur les Rudistes recueillis dans les couches crétacées des Corbiéres, B. S. G. Fr., (3), Vol. 20, pp. LA XX, 1892. (oriopleura, Toucasia, Polyconites, Caprina, Caprinula, many Caprotines and Hippurites). Sur la présence d’Hippurites au col de l’Argentitre. dem, (3), Vol. 24, p. 24, 1896. Présentation d’un mémoire sur les Hippurites de la Province orientale. /dem, (3), Vol. 24, p. 453, 1896. Sur les couches 4 Rudistes du Texas. /dem, pp. 387-388, 1808. Ktudes sur les Rudistes. /d¢d., pp. 140-156, 1898. (Good discussion of the canals). Sur quelques Rudistes Americains. /dcm, Vol. 28, pp. 205-221, 1900. Sur la Distribution Géographique des Rudistes, des Orbitolines et des Orbitoides. Idem, Vol, 28, pp. 222-226, 1900. Classification des Radiolites. /den7, (4), Vol. 2, pp. 461-477, 1902. Sur un Nouveau Genre de Radiolites, /d7d., pp. 477-482, 1902. Sur quelques Rudistes 4 Canaux. /dem, (4), Vol. 4, pp. 519-538, 1904. (MWitrocaprina, Rousselia, Caprinula, Polyptychus, Radiolitela). Les Explorations de M. de Morgan en Perse. /dem, (4), Vol. 4, pp. 541- 551, 1904. (Rudistid fauna included ). Les Rudistes d’Egypte. /dem, Vol. 9, pp. 77, 1909. (Preradiolites). Ktudes sur les Rudistes: Rudistes de Sicile, d’Algéria, d’Egypte, du Liban, et de la Perse, Mem. 41, Mem. Soc. Géol. de France, Pal., Vol. 18, 1y10. (AHippurites, Caprines). Pseudotoucasia et Bayleia, B.S. G. Fr., (4), Vol. 11, pp. 193-194, ror. Sur quelques Rudistes du Liban et sur l’évolution des Biradiolitinés. /dem, (4), Vol. 13, pp. 409-421, 1913. (Diéstefanella, Biradiolites). Les Requinéidés et leur évolution. /dem, Vol. 14, pp. 383-389, 1914. Reguienia, Toucasia). Les Rudistes de Turkestan, /ézd., pp. 390-396, 1914. (Radzolites). Les premiers Lapeirousia, C. R. Somm., B.S. G. Fr., Mar. 1, 1915. Sur l'appareil cardinal des Chama. /dzd, April 26, 1915, pp. 74-75, 1915. Le Barremien supérieur de Brouzet (Part III,Mem. 52, Les Rudistes). Mem. Soc. Géol. de France, Pal., Vol. 22, 1918. Regutenta, Monopleura, Agria). Emory-Conrad: Report on the United States and Mexican Boundary Survey, Vol. 1, Part II, 1857. (Description of Cretaceous and Tertiary Fosstls by T. A. Conrad, [be Leave). Felix: Versteinerungen aus der mexicanischen Jura- und Kreide-Formation. Palzon- tographica. Vol. 37, pp. 146-199, 1891. (Monopleura). 20 PALHONTOGRAPHICA AMERICANA 138 Studien tiber die Schichten der oberen Kreide-formation in den Alpen und den Mediterrangebieten. /dem, Vol. 54, pp. 251-339, 1908. Fischer: Manuel de Conchyl. 1887. Paris. Futterer: Die Gliederung der oberen Kreide in Friaul. Sitzungsberichte der. Kel. Preuss. Akad. d. Wiss. zu Berlin., Sitz. der physikalisch-mathem. Classe vom. 20 (Oct. Ny 18935 berline Gemmellaro: Caprinellidi della Zona superiore della Ciaca dei Dintorni di Palermo. Atti dell’Ac. Gioenia di Sci. Nat. di Catania. Second Series, Vol. 20, 1865, (Spherucaprina). Heilprin: The Geology and Paleontology of the Cretaceous Deposits of Mexico. Proc. Phil. Acad. Nat. Sciences, Vol. 42, 1890. (Mentions presence of rudistids). Hill: The Invertebrate fossils of the Caprina Limestone beds. Proc. Biol. Soc. Wash., Vol. 8, pp. 106-108, 1893. (Radiolttes). Matheron; Rech. pal. dans la midide la France., 3rd part, 1879. (JZatheronia). Mortillet, de: Fossiles nouveaux de la Savoie, B. Assoc. Florimont, Vol. II, p. 69, 1856. Munier-Chalmas: Prodrome d'une classification des Rudistes, Jour. de Conchyl., (3), Viole Xexel peet=7/5 morse Etudes critiques sur les Rudistes. B.S. G. Fr., (3), Vol. 10, p. 472, 1882. Observations sur les Rudistes, B.S. G. Fr., Vol. 16, pp. 819-820, 1888. (S¢rat#i- grapic distribution of Caprines and other rudistids in France and Greece). D'Orbigny: Quelques considérations zooligiques et géologiques sur les Rudistes, Ann. Se: Nat.; Wolf 17, 1842: Paléont. Fr. Terr. crét., Vol. 4, 1847. (Caprina, Regutenta, etc.). Paquier: Sur quelques Chamide’s de 1’Urgonien, B. S. G. Fr., (3), C. R. Somm., March 4, 1894. (Brief communication). Sur quelques Rudistes nouveaux de l’Urgonien. C. R. Ac. Sc., May 26, 1896. Sur la presence de Caprininés dans l’Urgonien. /dem., June 15, 1896. Sur quelques Diceratines nouveaux du Tithonique. B.S. G. Fr., (3), pp. 843-851, Vol. 25, 1897. (Aypelasma, Monnieria, Heterodiceras). Sur la presence du genre Caprvina dans |’Urgonien. C. R. Ac. Sc., Feb. 28, 1gor. 139 RUDISTIDS OF TRINIDAD 21 Comparaison des Rudistes urgoniens de Bulgarie et de France, B. S. G. Fr, (4), Vol. 1, p. 286, rgor. Sur la faune et l’dge des calcaires 4 Rudistes de la Dobrogea, /béd., p. 473, 1g0r. Sur les Relations du Groupe inverse avec le Groupe normal chez les Chamacées. Tbid., p. 474, Igor. Sur les Rudistes de l’Urgonien de Serbie. /dem., Vol. 8, p. 508, 1908. (Reqguienia, Toucasta, Monopleura). Paquier and Zlatarski: Sur l’Age des couches urgonieunes de Bulgarie. Jdem., p. 286, IgOl. Parona: Rudiste diS.Polo Matese. Mem. Ac. r. Torino, 1900-1901. Sopra alcune Rudiste Senoniane dell’ Appenino meridional. /ézd., Series 2, Vol. 1, 1900. Sopra alcune Rudiste del cretaceo superiore del Casiglio nelle Prealpi veneta. /dem, II, LIX, p. 139, 1908. (Aippurites). Nouvi Studii $. Rudiste dell’ Appenino. J/dem., p. 283, 1910-11. Pethoe: Die Kreide-(Hypersenon-) Faune des Peterwardeiner (Petervarader) Gebirges (Fruska Gora), Palzeontographica, Vol. 52, pp. 161-331, 1906. Pocta: Ueber Rudisten, eine ausgestorbene Famille der Lamellibranchiaten, aus der boehmischen Kreideformation. Prague, 1889. (Résumé in German; Fefalo- dontia). Roemer: Die Kreidebildungen von Texas und ihre organischen Einschliisse. Bonn, 1852. Sharpe: The Secondary Rocks of Portugal. Quart. Journ. Geol. Soc. London, Vol. 7, Part II, pp. 178-180, 1851. (Caprinula). Di Stefano: Part I: Gli strati con Caprotina di Termini Imerese. Atti. d. r. Ac. di Sc. Lett. e Belle Art. di Palermo. Vol. X, 1888. (Caprotines). Studi stratigrafici e paleontologici sud sistema cretaceo della Sicilia. (Part II), Palzeontographica Italica, Vol. IV, 1898. (Polyconttes. Many references). Stevenson: Some upper Cretaceous Shells of the Rudistid Group from Tamaulipas, Mexico. Proc. U. S. Nat. Mus., Vol. 61, Art. 1, pp. 1-28, 1922. Tocas: Etudes sur la Classification et 1’volution des Hippurites. Mem. 30, Mem. Soe. Géol. de France, Pal., Vol. 11, 1903; Vol. 12, 1904. 22 PALAONTOGRAPHICA AMERICANA 140 Sur la Classification et I’Fyvolution des Radiolitidés. /dem, Vol. 5, pp. 523-525, 1905. (Good brief summary’) Etudes sur la Classification et 1’ Evolution des Radiolitidés, Mem. Soc. Géol. de France, Pal., Mem. 36, Vol. 14, 1907; Vol 16, 1908; Vol. 17, 1909. (Vol. rg contains an extensive bibliography). Sur les Rudistes de la Serbie. B.S. G. Fr., (4), Vol. 8, p. 453, 1908. (Happurites). Sur les formes primitives des Hippurites dans les Préalpes vénitiennes. /did., p. 452, 1908. (Orbignya). White: On New Cretaceous fossils from California, Bull. 22, U. S. G. S., 1885. (Coralliochama) . Whitfield: Descriptions of species of Rudistee from the Cretaceous rocks of Jamaica. Am. Mus. Nat. Hist., Bull., Vol. 9. pp. 179-184, 1897. Zittel: Die Bivalven der Gosaugebilde, Denkschr. Akad. Wiss. Wien, Vol. 24, 1864. Text-book of Paleontology (Eastman). 1913, London. Zlatarski: Geol. Untersuchungen im Centralen Balkan und in den angrenzenden Gebieten. Sitzungsb. d. K. Akad. d. Wiss. Math. Naturw. Class. Wien, XCIII, I Abth., p. 312, 1886. — Rupistips OF TRINIDAD — Plate I (XVIII) 23 24 PALAONTOGRAPHICA AMERICANA 142 EXPLANATION OF PLATES Plate xr (XVIII) Amphitriscolus \waringi; sn. gens ne spi (Nats Size) \i.c.cer..oancsessoesneesesstcesecesslisvacceeuserceseceseserees Page 12 Type specimens; shown as excavated from the matrix, nearly in position of growth. The specimen in the foreground has been broken, showing the body cavity and some additional cavities or canals. The comimissure is about opposite where the shell is freed from the rock. ‘The section shown as fig. 4, pl. 4 was made half-way from the commissure to the apex of the upper valve. The lower valve is curved in the plane of the illustration, while the upper is curved away from the observer. The less curved shell, more in the background, shows very well the sudden in- crease in diameter about one and a half centimeter below the commissure. Fig. 5 of pl. 4 represents a cross-section made of the lower valve of this specimen just above where it is free from the matrix. Both figures 4 and 5, show a great amount of filling in of the various cavities in the sections remote from the commissure. See other more typical cross-sections, plate 4. ee —_ ae alas JPHGAGIO. I. WOE. ill, PALMONTOGRAPHICA AMERICANA, INO! 3h rset HAKRIS photo. et collo. Plate 2 (XIX) eran a) int eA Ta da ier ar Oia te 26 PALAONTOGRAPHICA AMERICANA 144 Plate 2 (XIX) Amphitrisceelus waringi, n. sp. (Nat. size) Figs. 1-3, upper valves ; 4-6, lower valves. Fig. 1, though an upper valve, is coiled about a foreign object. Fig. 2 shows well the twisting of valves, whether upper or lower. Fig. 4 shows the usual mode of growth of the long, more regular forms. The attach- ment is by the side of the tip turned away from the observer. Notice the position of the ligamental groove, Fig. 5 shows a common small form with flaring upper section. The amount of twisting from beak to commissure in these short specimens seems quite equal to that shown by the longer forms. Fig. 6 shows besides the lower valve a short portion of the upper valve, with canals. Notice the change in direction of the shell axis as the commissure is passed. Praise ro, VOL. 2, PALAMONTOGRAPHICA AMERICANA, ING, 3, IBeAise 2 HARRIS, photo. et collo. te ~ PALASONTOGRAPHICA AMERICANA 146 Plate 3 (XX) Amphitnisccelus\waningiy: ny isp2...