MIOCENE MOLLUSOA AND CKUSTACEA. 69 



The form is more inequilateral than that of Venus mercenaria, and the valve 

 is more inflated and proportionally longer anteriorly. The same remarks 

 apply equally well to its relations to M. Ducateli Conrad, which is 

 much more nearly related to V. (Mercenaria) mercenaria than is this one. 

 Besides the difference in form and ventricosity, the surface of this shell is 

 quite distinct from that of V. mercenaria, being marked by rather small, 

 appressed, and somewhat wrinkled concentric ridges, with very narrow 

 interspaces. These are crossed and cancellated by less distinct, radiating 

 impressed lines, which are closest and most distinct on the anterior part 

 of the shell and crenulate the margin. On the older, thickened part of the 

 shell, bordering the margin, the concentric lines are small and very much 

 crowded, presenting a distinctly old-age feature. Beyond the difference in 

 outline, the greater rotundity, and the surface markings there are no fea- 

 tures to distinguish it, as the interior, aside from the features of the hinge, 

 do not present differences from our common clam of the markets. 



Locality: The specimen, which is marked on the inside in ink, with the 

 name, is also marked "Type" and " Miocene, N. J." But under the descrip- 

 tion of the species Mr. Grabb refers back to other species found with this 

 specimen, where we find the locality given as "Shiloh, Cumberland County, 

 N. J." It is somewhat strange that among the other collections made in 

 that vicinity no fragment of it even has been noticed; consequently it may 

 be inferred that it is a very rare form. 



Mercenaria plena. 



Plate xn, figs. 4-6. 



Mercenaria plena Conrad; Am. Jour. Conch., vol. 5, p. 100. 



Venus plena (Con.) Heilprin; Tert. Geol. U. 8., p. 8; Acad. Nat. Sci. Phil., 1887, pp. 

 397 and 403. 



" Cordate, inequilateral, ventricose, oblique, with close concentric 

 rugose lines; posterior side subcuneiform ; lunule ovate; inner margin 

 densely crenulated." (Conrad). 



In his observations on this shell Mr. Conrad says : "It approximates 

 M. capax Conrad, but is shorter, less ventricose, more oblique; the hinge 

 character differs, and the pallial sinus is deeper and more angular." 



