268 Thirty-fifth Keport ok the State Museum. 



terior to the middle of the shell and of the hinge-line. Anterior ear 

 small, triangular, with a longitudinal fold ; limited by a broad 

 sulcus; margin slightly convex; extremity acute. Posterior ear 

 large, broad-triangular, undefined ; margin slightly concave, ex- 

 tending at right angles fco the hinge, to the post-basal side of the 

 valve ; extremity angular. Byssal sinus broad in the left valve. 



Test thin, marked by fine, alternating, filiform, radiating striae, 

 which increase by implantation until they are very numerous at the 

 basal margins of some specimens, crossed by fine lines of growth 

 with a few concentric undulations. The ears preserve the same 

 surface characters in a subdued degree. Many of the specimens 

 are exfoliated and the surface markings are very obscure or obsolete. 



A specimen of the left valve has a length of 14 mm., height 12 

 mm., hinge-line 16 mm. A larger example has a length of 19 mm., 

 height 16 mm., and hinge-line 21 mm. 



This species was arranged with P. conspectus. The recent study 

 and comparison of a more numerous series of specimens show several 

 important differences, and necessitate the removal of this form 

 from that species. The present species is more oblique, narrower, and 

 the posterior ear is comparatively longer than in authentic forms of 

 P. conspectus. In P. Hermes the hinge-line is more extended poste- 

 riorly, and the umbonal angle more obtuse, while in P. regularis the 

 hinge is shorter, the extremity of the posterior ear rounded, and the 

 margin continuous with the curvature of the pallial margin of the 

 valve. 



Formation and localities. In the shales of the Hamilton group at 

 Ludlowville, Tompkins county, and on the shores of Cayuga and 

 Canandaigua lakes, N. Y. 



Pterinopectek regularis. 



Pterinopecten regularis, Hall. Pal. N. Y., vol. v, pt. 1, fig. 1. Unpublished. 



Shell of medium size, semi-circular ; body of the valve oblique ; 

 length nearly one-fifth greater than the height, greatest lengi^i above 

 the middle ; margins very full and regularly rounded from the byssal 

 sinus to the posterior extremity of the hinge. Left valve moderately 

 convex. Eight valve unknown. Hinge-line straight, anterior; 

 length a little greater than the length of the valve. Beak of left 

 valve acute, directed forward, situated anterior to the middle of the 

 hinge. Anterior ear small, triangular, more than half as long as 

 the posterior ear, limited by a broad sulcus ; margin convex ; ex- 

 tremity rounded. Posterior ear large and undefined from the body 



