170 PAL^OI^TOLOGY OF NEW JEESEY. 



The surface markings are very fine, and represent lines of growth only. It 

 is probable that some of the many small indistinct casts from the micaceous 

 clays beneath the Lower Green Marls at the Rev. G. C. Schanck's pits, near 

 Marlborough, N. J., may belong to this species ; but so far I have not seen 

 anything so transversely elongated. 



Formation and locality. — The specimen above described is from Had- 

 donfield. New Jersey, from the micaceous clays at that place. 



Genus COEIMYA Agassiz. 



Corimya tenuis, n. sp. 

 Plate XXIII, Figs. 9-11. 



Shell small in size, the largest individual cast observed measuring 

 scarcely one and a quarter inches in length. Form triangularly-elliptical, 

 with nearly central beaks, from which the cardinal margins slope rapidly 

 on each side, the extremities being nearly equally rounded, but the posterior 

 narrower than the anterior, and the postero-cardinal margin very slightly 

 contracted near the beaks. The valves have been depressed convex, unequal 

 and slightly twisted, the right valve less convex than the left, and its basal 

 margin concave as viewed on the basal edge. Surface of the cast marked 

 by concentric undulations, indicating a somewhat distinctly undulated shell 

 surface. Muscular scars as indicated on the casts rather large, the posterior 

 one bounded on its inner side by a depressed groove indicating a ridge on 

 the inside of the shell; much the strongest on the right valve. No evidence 

 of a pallial sinus has been seen on any of the specimens. The surface of 

 the disk of the cast, on those which indicate a thickening of the shell, is 

 marked by radiating vascular lines, most distinct on the posterior side of the 

 beaks, and evidences of a few radii on the anterior third. 



I'he internal casts of this species are not uncommon at several locali- 

 ties of the Lower Marls, and are extremely JfeZ/ma-like in their characters 

 and appearance. They occur of all sizes, from half an inch in length to 

 that of the largest one above mentioned, and are usually thin, flattened 

 specimens, often with but little character by which they can be recognized. 

 The more ventricose and larger individuals closely resemble casts of Peri- 



