274 Thirty-fifth Report ok the State Museum. 



Formation and localities. In the Chemung group at Belmont, Alle- 

 ghany county, N. Y., and Mansfield, Tioga county, Pa. 



Pterinopecten erectus. 



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 Unpublished. 



Shell above medium size, transversely semi-elliptical, scarcely oblique; 

 length and height nearly equal; pallial margins regularly rounded, 

 slightly extended on the posterior side. Valves moderately convex. 

 Right valve apparently more convex than the left ; the differences 

 between them have not been satisfactorily determined. Hinge-line 

 straight, length a little greater than the length of the shell. Beak 

 small, acute, directed forward, little, elevated above the hinge- 

 margin ; anterior to the middle of the shell. Umbonal region not 

 defined. Ears triangular, unequal. Posterior ear large, undefined; 

 margin slightly concave ; extremity acute. Anterior ear much 

 smaller, not defined; margin concave; extremity acute. Byssal 

 sinus shallow. 



Surface marked by numerous rounded unequal radii; the larger 

 ones alternating with one, two or three smaller ones; crossed by 

 fine, sharp, regular, concentric strias of growth. On the ears the 

 striae are fine and uniform. Ligamental area narrow. The largest 

 specimen has a length of 32 mm., height 30 mm., hinge-line about 

 34 mm. 



There is some resemblance between this species and P. dispandus, 

 but it differs in its comparatively smaller size, longer hinge-line, and 

 somewhat less oblique form. 



Formation and locality. In the shales of the Chemung group at a 

 point 600 feet above the base of the formation, at Ithaca, N. Y. 



Pterinopecten crenicostatus. 



Pterinopecten crenulatus (by error), Hall. Pal. N. Y., vol. v, pt. 1. Plates and 

 Explanations : PI. 8, figs. 3, 4. Jan., 1883. 



Shell large, sub-orbicular, slightly oblique; length somewhat greater 

 than the height; pallial margins regularly curved, broadly rounded 

 from the anterolateral to the basal margin ; post-lateral margin 

 less convex. Left valve very moderately convex. Eight valve not 

 known. Hinge-line straight, length one-fifth less than the length 

 of the shell, extended anteriorly, but not as far as the anterior 



