p. 73-76, [2] leaves of plates : ill. ; 24 cm.Includes 1 bibliographical reference (p. 73)

Brown, Barnum.

Whitfield, Robert Parr, 1828-1910.

American Museum of Natural History Scientific Publications

Article VI.-DESCRIPTION OF A NEW TEREDO-LIKESHELL FROM THE LARAMIE GROUP.By R. P. WHITFIELD.PLATES XXVIII-XXIX.A block of coniferous wood, highly mineralized (calcareous),was brought in from the east side of Alkali Creek, Wyo., 35miles west of Edgemont, S. D., in I900 by Mr. BarnumBrown of the Museum Expedition. The bed from which itwas obtained is near the top of the Laramie Group, andknown as the Triceratops Bed. The wood contains a groupof the casts of borings of a very large species of Teredo-likeshell, several of which measure about one and a quarterinches in diameter at the larger end, or near the end of theboring, at the point where the shell is located. A numberof these retain remains of the shell well enough preservedfor description and partial if not complete illustration. Theblock when first obtained was quite bulky, being eight orten inches high and wide by a foot in length, but in freeingthe cast of the borings from the matrix so that they could bestudied and illustrated, it was necessary to reduce it con-siderably; so that only the portion containing the boringsis preserved, of which the photographic plate given to illus-trate it is just half-size. The block as it now remains containsthirteen of the borings more or less entire, with evidence ofat least five others. There are also quite a number of otherspecimens which were detached from the block at the time itwas collected.In studying the characters of the shell as seen in specimensmore or less freed from the matrix, but greatly exfoliated,it would appear that the shell is more closely allied to thegenus Turnus of W. M. Gabb, as emended and illustrated byF. B. Meek, in Vol. IX of the Report of the United StatesGeological Survey of the Territories, and by F. Stoliczka andTryon, than any other of the known genera of this group of[73]74 Bulletin American AMuseum of Natural History. [Vol. XVI,shells. Its great size, however, is somewhat startling as com-pared with the allied forms, which are minute, while this at-tains a transverse diameter of one and three eighths of aninch through the valves.The valves have the feature of the rectangular notch inthe anterior border, with a large shield-shaped piece fillingthe hiatus, which forms a section of a sphere, and is, so faras can be ascertained from the specimens, quite smooth, i. e.,destitute of surface corrugations. The valves have the usualoblique radiating sulcus passing from the beaks to the ex-treme basal point, and a secondary fainter one passing infront of the beaks to the angle of the rectangular notch; theyalso show the concentric lines parallel to the margins of theshell, so characteristic of the Teredinae. The best preservedspecimens show also the thin posterior prolongations of thevalves into the tube to a length of over two inches beyondthe posterior margin of the valves proper, giving a total length,in the specimen photographed for illustration, of three andone fourth inches. All of these features, except perhaps thethin posterior prolongation of the valves, are features whichpertain to the genus Turnus as illustrated by the authorsabove mentioned. But beyond this I find, a little anteriorto the beaks, evidence of a thickened hinge-plate which isdivided into four small teeth on the right valve, which areopposite to and probably fitted into similar ones on the othervalve. No appearance of a hinge structure posterior to thebeaks has yet been observed.There is unmistakable evidence of a thin shelly lining tothe tube for some distance beyond the thin prolongation ofthe valves.In most of its features, this Laramie shell resembles theCretaceous Turnus elegantulus Meek, but it is more gapingbehind, and the anterior rectangular hiatus is closed by ashield-shaped plate. It is certainly destitute of the internalridge which is supposed to be a principal feature of that shell.From the living form, Jouannetia, it differs in the widelygaping posterior end, although apparently extended bysmooth secretions of shelly matter, and materially so in itsWhitfield, A New Teredo-like Shell.equivalve shell. From Meek's Goniochasma and others itdiffers in wanting the internal ridge behind the beaks. Itherefore propose for it the generic name Xylophomya, andgive below a diagnosis of the generic characters observed.Xylophomya, gen. nov.Generic description.-Burrowing bivalve shells, widely gaping pos-teriorly, with a deep rectangular notch or hiatus in the anterior bor-der. Basal margin prolonged into acutely triangular extensions.Valves marked by a narrow sulcus from beak to base and by a secondfainter one anterior to it, reaching the margin at the angle of thehiatus. Hiatus filled by a broad shield-like plate. Hinge-plate di-vided, anterior to the beaks, into four minute tooth-like denticles onthe right valve. Posterior margin of the valves prolonged in a smoothtongue-shaped extension, filling the diameter of the burrow, andapparently connecting with the lining of the tube.Xylophomya laramiensis, sp. nov.PLATES XXVIII-XXIX.Shell large for the group, measuring one and a fourth inches indiameter, burrowing in wood or other substances; very ventricoseand the valves extended backwards into the tube to the extent of twoinches or more, gradually narrowing posteriorly, rounded behind.Surface of the valves marked with close concentric lines parallel tothe margins. The anterior plate shield-shaped, broad, smooth on theexterior, as are also the posterior extensions of the valves.Locality and Formation.-Alkali Creek, Wyoming, 35 miles west ofEdgemont, S. D., in strata of the Laramie Group. Collected by Mr.Bamnum Brown.While examining these western forms I tried to find theplate filling the anterior rectangular hiatus in 7urnus ele-gantulus Meek on specimens in an original block in the HallCollection, but obtained only negative evidence.Just after working out the block of this western form thatserved for the photograph illustrating the species I made avisit to the Cretaceous beds at Atlantic Highlands, N. J., andpicked up a small slab evidently from the yellow sands atI 902.] _' r76 Bulletin American Museum of Natural Histoty. [Vol. XVI.]the top of the hill, and found that it contained four more orless perfect casts of a Teredo-boring very closely resemblingCasts of Teredo-borings from the Cretaceous beds at Atlantic Highlands, N. J.the western ones. The outline figure here given is madefrom it.EXPLANATION OF PLATE XXVIII.Xylophomya laramiensis, page 75.View, one half diameter of the original block after the wood had beencut away between and from around the burrow fillings.fri04z.4I.''4'46xrs3dEXPLANATION OF PLATE XXIX.Xylophomya laramiensis, page 75.FIG. i.-Back view, nat. size, of one of the separated burrows, whichretains a portion of the shell showing the oblique umbonalfurrow and the prolonged extension of the shell to thepoint marked a.FIG. 2.-Side view of the same specimen.FIG. 3.-Back view of a second individual which shows the shell tohave extended to the point a.FIG. 4.-A restored drawing of the anterior end of the specimenshown in Fig. i, giving the form of the anterior shield-shaped plate and the anterior notch in the margin of thevalves.FIG. 5.-Lateral outline view of the valve, showing the markings ofthe surface as obtained from several specimens.FIG. 6.-Outline showing the form of the valve.FIG. 7.-Outline figure of the dorsal view of the end of the specimenFig. i to show the extent of the shell proper, to the be-ginning of the posterior extension.FIG. 8.-View of the anterior teeth as seen on a fragment chippedfrom between the beaks, 3 x.BULLaTIN A. M. N. H.o.1VOL. XVI., PL. XXIX.7- '- -,el8.2HELIOTYPE 00., BOSTON.NEW TEREDO

New Teredo-like shell

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