MIOCENE MOLLUSCA AND CRUSTACEA. 55 



served in the Academy of Natural Sciences at Philadelphia. The specimen 

 is considerably waterworn, so that the teeth and the marginal crenulations 

 are worn away, but the exterior markings of the shell are still plainly 

 visible, leaving no doubt of the specific identity. 



ASTARTE THOMASI. 



Plate vin, Figs. 3-7. 



Astarte Thomasi Conrad; Proc. Acad. Nat. Sci., Phil., 1855, p. 267; Am. Jour. Conch., 

 vqI. 2, p. 72, PI. iv, Fig. 1G; Proc. Acad. Nat. Sci. Phil., 1862, p. 578; Meek, 

 Check List Miocene Foss., p. 7; Heilprin, Cont. Tert. Geol. and Pal. U. S., p. 8; 

 Proc. Acad. Nar. Sci., 1887, pp. 400 and 402. 



t Astarte exaltata Heilprin; Cont. Tert. Geol. and Palaeont. U. S., p. 8. 



" Triangular, not ventricose, inequilateral; ribs concentric, robust, 

 recurved; concentric lines more or less marked, minute; toward the poste- 

 rior ends the ribs suddenly become obsolete; extremity truncated, nearly 

 direct, or sloping inwards; inner margin crenulated; lunule large, ovate, 

 acute, deeply excavated." (Conrad in Proc. Acad. Nat. Sci. Phil., vol. 7, 

 p. 267.) 



This species somewhat closely resembles the recent Astarte castanea of 

 our own coast, but is somewhat smaller generally, and less arcuate. The 

 shell is ovately triangular, longer than high, and moderately convex; the 

 beaks prominent pointed and well directed forward. The concentric ribs, 

 15 to 20 in number, are rounded on the surface or slightly arched back- 

 wards, and are concentrically striate on their surfaces. The lunule is deep, 

 elongate-ovate in form, and pointed below; the escutcheon is deep and nar- 

 rowly lanceolate in form, both being somewhat variable in different indi- 

 viduals. The substance of the shell is thick and heavy, and the muscular 

 imprints in the interior are large and strongly marked. Hinge plate small 

 and narrow, crenulations of the inner border rather coarse and deeply 

 marked. 



The species is most nearly allied to A. exaltata Con. (Medial Tert., p. 

 66, PI. xxxvn, Fig. 6) of any fossil form of the Miocene deposits, but it is 

 more triangular, less rounded on the base, and not so deeply arcuate ante- 

 rior to the beak. The surface structure, however, is quite distinct; that one 



