p. 623-628, [5] leaves of plates : ill. ; 24 cm

Brown, Barnum.

Whitfield, Robert Parr, 1828-1910.

American Museum of Natural History Scientific Publications

56.4,1U(117:78.6)Article XXVI.- REMARKS ON AND DESCRIPTIONS OF NEWFOSSIL UNIONIDAE FROM THE LARAMIE CLAYSOF MONTANA.BY R. P. WHITFIELD.PLATES XXXVIII-XLII.The few species of Unio included in this article are from the Laramieclays, 130 miles northwest of Miles City, Montana, from a bed located about180 feet above the Fort Pierre shales, and consequently well above therecognized Cretaceous horizon.The shells are fairly well preserved and retain the nacreous coloring to agreat extent, though the outer epidermal coating is usually absent and notinfrequently the prismatic outer layer is partly absent or frequently crumbleson being washed. The clay beds in which they are found are horizontal,and usually undisturbed, except by the weathering and washing consequentupon the weathering.These shells are from near the same locality as the six species describedin Volume XIX of this Bulletin (pp. 483-487), but come from a somewhathigher level above the Pierre, being at about 400 feet above the shale.Among those previously described, three of the species so closely resembleliving species known from the western river water-shed, that I gave themnames indicating these resemblances. In this lot occur four others thathave similar resemblances, namely, U. bikesopoides from U. w8opoide8 of thefirst lot, differing from it in having a double line of nodes along the umbonalslope, instead of only one. The others resemble respectively U. pyramidatus,U. cylindriCus, U. cornutus and U. gibbosus.Among other species common in the same localities and clays one of themost abundant forms is usually referred to U. dane Meek and Hayden butwhich I think is much more closely allied to Unio gibbo8us Barnes, of theOhio and Mississippi Rivers. It differs materially from Meek's figures ofU. dane, in not possessing the radiating strie shown quite conspicuouslythere as given in Vol. IX, Geol. Surv. Territories, pl. 41, figs. 3a and 3c, butdo not appear on C. A. White's fig. 2a, plate 27, Contributions to Palaeont.,1880, but do appear on those copied from Meek's in White's, 'Non MarineMollusca', Third Ann. Rept. U. S. Geol. Surv., 1881-82, pl. 17, figs. 1 and 2,but again do not on those given on pl. 18, figs. 1 and 2.These Laramie shells from this Montana locality, are so closely similar623Bulletin American Museum of Natural History. [Vol. XXIII,to those from the Ohio River localities that I propose to designate them by thename U. gibbosoides.Considering all the similarities between these Laramie fossils and theirrepresentative species in the Mississippi and Ohio water-sheds, I ventureto state that these further western waters of the Laramie times- were theoriginal home of much of the Unio fauna of these more eastern recent local-ities.From this locality, 130 miles northwest of Miles City, Montana, we havethe following species, represented by closely allied forms, some of them sonearly like the living species, that it would do but little violence to specificfeatures, to state they were the same, namely:Unio wsopiformis resembles U. Wsopus Green.Unio letsoni " U. cornutus Barnes.Unio cylindricoides ' U. cylindricus Say.Unio gibbosoides " U. gibbosus Barnes.Unio pyramidatoides " U. pyramidatus Lea.-Unio retusoides " U. retusus Lam.Unio verucoiformis U. verrucosus Barnes.Unio biesopoides, n. sp.PLATE XL FIG. 7, and PLATE XLI, FIG. 8.Shells like those of U. acsopoides in all essential particulars, internal and external;except that it presents two distinct lines of nodes leading from near the beaks back-wards to the posterior basal angle instead of only a single line of nodes as also in therecent or living species U. exsopus, the second line being on the umbonal angle.Locality and formation.- Laramie beds, 130 miles northwest of MilesCity, Montana, 180 feet above Pierre shales. Barnum Brown, collector.Unio pyramidatoides n. sp.PLATE XLI, FiGS. 1-5.Shell somewhat resembling the living U. pyramidatus in general features, butmore erect, narrower across the body of the shell, in an anterior-posterior direction,and without the su1cus on the posterior umbonal slope; or at least having it lessdeveloped or very narrow and shallow, while the posterior margin is flattened andthe umbonal ridge decidedly angular and often subcarinate; the lunule being quitesmall or usually nearly obsolete, and the beaks, when not eroded, show a decidedzigzag or doubly V-shaped system of corrugation. Internally the shells are remark-ably heavy and thickened, making the teeth and all internal features even largerand proportionally thicker and deeper than in the living representative species.The posterior lateral teeth are usually more curved.624Whitfield, New Fossil Unionidwe.Locality and formation.- Laramie beds, 130 miles northwest of MilesCity, Montana, 180 feet above Pierre shales. Barnum Brown, collector.Unio pyramidellus n. sp.PLATE XL, FiGs. 3 AND 4.Shell small, very erect, from beak to base, and mostly less than one and onefourth inches high; disc of the valves rather depressed convex, with a slight sulcuscrossing from the beak to the posterior angle quite near the posterior margin. Beakproportionally heavy, tumid, directed forward; anterior margin slightly concave,posterior margin slightly convex, basal margin broadly rounded. Internal featuresthickened, hinge plate and lateral tooth in the right valve large, the plate broad andslightly concave in the best preserved valve, and the lateral tooth much curved andthickened. Cardinal tooth triangular, proportionately large, cuneiform above, belowdivided by three vertical grooves, the socket having four ridges to fit against thelarge tooth of the opposite valve. Anterior muscular impression small, but deep,the secondary small and shallow, close to the former. Posterior impression long,narrow and moderately distinct. Surface of the disc smooth except for distinctgrowth lines.The shells are poorly preserved and mostly much distorted by compres-sion, but all show a much, bent hinge plate and strong teeth, the cardinaltooth being low down near the- middle of the anterior border, and the longlateral tooth and posterior scar extending below the middle of the height.Locality and formation.- Laramie beds, 130 miles northwest of MilesCity, Montana, 80 feet above Fort Pierre shales. Barnum Brown, collector.Unio gibbosoides n. sp.PLATE XL, FiGs. 1 AND 2.Shell transverse, compressed, much wider than high, and resembling in nearlyall respects U. gibbosus of Barnes, as it occurs in the Ohio and Mississippi Riversat the present time, both externally and internally.It has been commonly referred to as U. dance Meek & Hayden which itclosely resembles, but it never shows the radiating strise which that speciesquite generally does, passing obliquely backward across the valves from thebeaks to the basal boarder along the depressed middle portion of the valves.In most other respects the two species are closely allied.Locality and position.- In Laramie Clay, about 120 feet above Pierreshales, on Snow Creek, on the Missouri River, in Montana.1907.] 625Bulletin American Museum of Natural History. [Vol. XXIII,Unio subtrigonalis n. sp.PLATE XL, FIGS. 5 AND 6.Shells small, triangular, ventricose cuneate, pointed behind, seldom exceedingan inch and an eighth in an anterior and posterior line, sharp and subangular on theumbonal ridge, with a nearly vertical posterior slope, which is slightly sulcated infront of the umbonal ridge; otherwise the disc is smooth or marked only by growthlines; base broadly rounded; beaks anterior, moderately heavy. On the interiorthe hinge plate is abruptly bent at some distance behind the beak, and the lateralteeth are thin and erect, while the cardinals are heavy and much corrugated. An-terior muscular imprint small but moderately deep, the posterior scar elongate,faintly marked and situated on the inside of the vertical cardinal slope.The species is exceedingly like Corbicula subtrigonalis C. A. White,externally; but is decidedly and unmistakably a Unio, and not a Corbicula.Locality and formation.- In Laramie ferruginous marls, 130 miles north-west of Miles City, Montana, 80 feet above Pierre shales. Barnum Brown,collector.Unio cylihdricoides n. sp.PLATE XXXVIII, FIGS. 1-7; PLATE XXXIX, FIGS. 1-3.Shell attaining a moderately large size, the adult shell being fully as large asfull-grown specimens of the living U. cylindricus, which it resembles in size, formand general features, except in lacking the characteristic sculpturing of the surface.The largest individual in the collection was, when entire, fully four and one fourthinches in length. The shells are externally decidedly elongate-rhombic, muchswollen along the umbonal ridge, which is sometimes quite angular. The beaks areenrolled and placed well forward, but not terminal, the outline of the figure beinghighest below the middle of the height anteriorly, while the living form is generallyhighest centrally. Posteriorly the reverse is the general rule in the fossil form,IWghest above the center and sharply rounded. The middle of the disc is broadlysulcated from the beaks to the basal margin, the sulcus covering the entire middlethird of the shell.No surface sculpturing exists on the larger specimens, but on the youngand medium sized individuals, there is a system of raised ridges indicatingor foreshadowing all of the markings of the. living examples of U. cylin-dricus, except the nodes on or near the umbonal ridge, posteriorly to the endof the shell.Internally all the features of the living form are present and so closelysimar that it seems unnecessary to recapitulate them.Locality and formation.- In muddy shales of the Laramie formation,130 miles northwest of Miles City, Montana, 180 feet above Pierre shales.Barnum Brown, collector.626Whitfield, New Fossil Unionidc.Unio letsoni n. sp.PLATE XLII, FIGS. 1-4.Shell rather below medium size for the genus, circular or broadly transverselyoval in outline, and quite ventricose, but not globular. Beaks moderately large,nearly central, slightly oblique and but little enrolled. Surface of the shells highlyornamented except on the antero-basal quadrant, where there are only strongconcentric lines of growth. Along the center of the valves from beak to base, thereruns a line of strong heavy nodes usually numbering four on adult shells, wherethe height from beak to base will be about or a little more than one and a half inches,or nearly four cm. where the transdiameter, from anterior to posterior of the out-line will be about, or over, four and a half cm., or somewhat more than one and three-fourths inches. Posterior to the median line of nodes and on the umbonal thirdof the shell there is always a double set of oblique depressed lines which give to thispart of the shell the structure of a very coarse file. On the posterior half of the shellthere is a system of oblique undulations or plicae, which extends from the posteriorside of the median line of nodes, gradually turning backwards and extending to theposterior margin of the valve and to the cardinal and basal edges of the shell, grow-ing larger with the increasing growth of the valve. On the larger valve figured,these plications are sixteen in number, those of the beak portion being quite smalland strongly curved towards the hinge. Between this set of markings and thecentral ridge there is usually another set of small ridges running between the start-ing of the posterior plic.s and the central ridge, passing from the ends of the posteriorridge towards the anterior basal border and forming with the posterior plice a seriesof very acute angles. These acute-angled ridges are most distinct on young individ-uals, often becoming faint from erosion on the older olnes. On a single youngindividual of about an inch in height, there occur two small accessory nodes on eachside of what would be the second node of the line on larger specimens.Interiorly the valves are deep, and of a brownish pearly color. The cardinalteeth are well developed, the hinge plate wide, the laterals curved and moderatelyhigh, and the space between the cardinals and the laterals somewhat flattened. Themuscular scars are distinct and rather deep.Locality and formation.- Laramie beds, 180 feet above Pierre shales,130 miles northwest of Miles City, Montana. Barnum Brown, collector.This species in many of its features somewhat closely resembles ortypifies U. cornutus Barnes of the Mississippi and Ohio water-sheds, andforms another species with closely related resemblances. The species isnamed in honor Dr. E. J. Letson, the eminent conchologist in charge of theCollection of the Buffalo Society of Natural History, Buffalo, N. Y.UnJio corbiculoides n. sp.PLATE XLI, FIGS. 6 AND 7.Shell small, rather below the average of the genus, subcircular in outline, ventri-cose, smooth, except for growth lines and two faint ridges shown on the posterior1907.] 627628 Bulletin American Museum of Natural History. [Vol. XXIII,cardinal slope and so obscure as to readily escape observation. A few faint corru-gations are seen on the posterior surface of the beaks. Length of the shell, fromthe anterior to the posterior margin, slightly exceeding the height from beak to base.Posterior margin slightly flattened verticaUly, which on single valves has a tendencyto give a somewhat subquadrangular outline, scarcely perceptible on the uncom-pressed shell. Lunular space deeply sunken, narrow, but very marked and dis-dinct; ligamental area deep, sharply margined. Beaks tumid when not eroded,faintly corrugated.Interiorly the hinge plate is strongly bent, the lateral teeth curved, the cardinalsstrong and proportionally heavy, none of them have these features well enoughpreserved to present details. Muscular scars faint and the shells rather thin.Locality and formation.- Laramie group, 130 miles northwest of MilesCity, Montana, 80 feet above Pierre shales. Barnum Brown, collector.EXPLANATION OF PLATE XXXVIII.UNIO CYLINDRICOIDES n. sp. Page 626.Fig. 1. View of the left valve, natural size, preserving a patch of the outsideshell.Fig. 2. Cardinal view of another specimen, natural size. The anterior end ofthe right valve is considerably broken. This shell probably being a female is muchmore ventricose than the other.Fig. 3. Cardinal view of a male shell. The shell has mostly lost the outerprismatic layer.Figs. 4-7. Views of four shells of different sizes or ages, oii which the naturalsculpturing is more or less preserved, but is not fully shown, as the photographsfail to show them. On the umbonal ridge the line of nodes was expected to bevisible but is not.VOL. XXIII, PLATE XXXVIII.S.4....A..v...I. .1.,1...I'lE W ;rI2'3-.t4:3--~.A;w:.N j.:..0..{e, oa...7 ._V2NEW FOSSIL UNIONIDu.BULLETIN A. M. N. H..'AAR:V..V,EXPLANATION OF PLATE XXXIX.UNIO CYLINDIROCOIDES n. sp. Page 626.Fig. 1. Left valve of the specimen shown in Plate XXXVIII, Fig. 2, naturalsize, showing the difference in what is supposed to represent a female form of thespecies; compare with Figs. 1 and 3, Plate XXXVIII. The outside of the shellihasthe surface more or less destroyed by decay.Figs. 2 and 3. Views of the interior of the valves, right and left, of the samespecimen represented in Fig. 1, where the outline is more or less restored. The figuresshow the teeth and muscular scars. Fig. 2 contained a partial cast of black chertwhen the photograph was made but which was subsequently removed.BULLETINA. M.N..H. VO. XX,, PLTXXX(: : ~~~~~~~~~~~~~~~~~~~~~. ..... ..<__nAX9 ..................5 ..f .........z.IiNEW FOSSIL UNIONIDA:.BULLETIN A. M. N. H. VOL. XXIII, PLATF, XXXIX.311",'I,i'W.., 4.'I .. )IM:... t J,4141. -.1411:L.fEXPLANATION OF PLATE XL.UNIO GIBBOSOIDES n. sp. Page 625.Fig. 1. Outside view, natural size, of an entire right valve, showing the generalfeatures.Fig. 2. View of the interior of another and slightly smaller valve.UNIO PYRAMIDELLus n. sp. Page 625.Fig. 3. Exterior, natural size.Fig. 4. Interior of the same specimen, natural size.UNIO SUBTRIGONALIS n. sp. Page 626.Fig. 5. Exterior view, natural size, of a very perfect valve.Fig. 6. Interior view, natural size, of the same valve.UNIO BIDESOPOIDES, n. sp. Page 624.Fig. 7. Interior view, natural size, of a nearly perfect large valve. For exteriorview see Plate XLI, Fig. 8.Ist,</,^2',.c y ,-,.....fi t; " "e .(4 -r w. < ,. tsN < )4*......IfK,-Ii..:iNEW FOSSIL UNIONIDAE.BULLETIiq A. M. N. H. VOL. XXIII, PLATE XL.EXPLANATION OF PLATE XLI.UNIO PYRAMIDATOIDES n. sp. Page 624.Fig. 1. Exterior view, natural size, of a left valve showing the general featuresof a narrow form of the species, and the corrugated beak.Fig. 2. Posterior view of the same, showing the flattened posterior side andligamental area.Fig. 3. Interior of a small valve of the species.Fig. 4. Interior of a left valve showing the very heavy cardinal tooth and thicklateral tooth.Fig. 5. Interior of a right valve of a larger individual showing the heavy cardi-nal tooth and the lateral with its corrugated ridge. This figure is of a somewhatbroader form than the others, but not as broad as some. The last three figures arefrom photographs and do not show the features intended to be shown.UNIO CORBICULOIDEs n. sp. Page 627.Figs. 6 and 7. Two views, natural size, of the only perfect individual of thespecies preserving the rotundity as well as all the markings of the species.UNIO BIESOPOIDES n. sp. Page 624.Fig. 8. View, natural size, of the exterior of a large entire valve, showing thedouble row of tubercles which characterize the species.VOL. XXIII, PLATE XLI...".....-.d- II..ima..T...1At,,X..Nl''.' r3*;,V',< ,_ .6,;C,/.,f ., o'.>" uo.w.x; , EaV i+A¢ -aqeN;C.. o>.... <A.,.'t4"7`1NEW FOSSIL UNIONIDAE.BULLETIN A. M. N. H.K.EXPLANATION OF PLATE XLII.UNIO LETSONI n. sp. Page 627.Fig. 1. View of a young individual entirely covered by the corrugations ofthe beak portion and only showing two of the central lines of nodes.Fig. 2. A somewhat older specimen showing three nodes on a line at the center.Perhaps only an abnormal feature.Fig. 3. View of an almost adult valve showing all the prevailing features ofthe species, including the central line of nodes which allies it to U. cornutus.Fig. 4. View of another and opposite valve showing four central nodes butmuch smaller in size; the third is only partially formed and marginal.UNIO VERRUCOSIFORMIS Whitf.See Bull. Amer. Mus. Nat. Hist., Vol. XIX, p. 484, pl. xl, fig. 10.Fig. 5. View of a medium-sized specimen, introduced to correct and explainthe imperfect figure in the previous volume of this Bulletin.Fig. 6. View of the inside of the same valve.This species has proved to be quite abundant and fairly well preserved, whereasthose in the collections of previous expeditions were very poor and scarce, and theone figured was the best obtained at that time. The shell is very rotund and thenodes and plications of the surface are distinct and often well shown.BULLETINA.MN.H VOL. XXIII, PLATE XLII.~~~~~L-3-NEw FossIL UNIONID4,BULLETiiv A. M. N. H. VOL. XXIII, PLATF, XLII.

New fossil Unionidae

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