L02 PALAEONTOLOGY OF NEW YORK. 



Line aboul 35 nun. A smaller specimen is 26 mm. in length, 25 mm. in 

 height, hinge-line "J 4 mm. 



This species bears a general resemblance to P. Chemungensis ; it differs in 

 its continuous and comparatively stronger rigid radii. The group of four species, 

 iK'ii-inning with P. Chemungensis, is well marked and have many characters in 

 common; but nevertheless, present differences which warrant their specific 



separation. 



Formation and localities. In the Chemung group, at several localities in 

 Chemung county, N. Y. 



Pterinea prora. 



Cl.ATi: XVI. FIGS. 4, 13, II. 



Pterinea prora, Hall. Pal. N. V.. vol. v. pt. 1. Plates and Explanations: PI. 16, figs. 4, 13. 14. 



Jan., 18S3. 



Shell of medium size or larger, sub-rhomboidal, oblique; body ovate, narrow 

 above; length one-fourth greater than the height; margins regularly rounded, 

 extended on the post-basal portion and sloping rapidly into the sinus of the 

 wing. 



Left valve moderately convex. Right valve depressed-convex above, Hat 

 or concave below, apparently smaller than the left. 



Hinge-line straight, longer than the length of the valve, and extending 

 beyond both margins. 



Beak small, acute, directed forward, situated at about the anterior fifth of 

 the hinge. Umbonal region undefined, not prominent. 



Ear about one-fifth the length of the wing, separated from the body of the 

 valve by a shallow undefined sulcus and marked byssal sinus; margin con- 

 vex; extremity rounded. Wing large, triangular, extended, defined only by 

 the change in the curvature of its margin from that of the body of the valve; 

 margin deeply concave; extremity acute. 



Surface of left valve marked with regular, rounded/sub-equal rays, with 



