102 
PALEONTOLOGY OF NEW YORK. 
line about 35 mm. A smaller specimen is 26 mm. in length, 25 mm. in 
height, hinge-line 24 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, 
beginning 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. 
PRATE XVI, FIGS, 4, 13, 14. 
Ptei'inea prom, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PL 16, figs. 4, 13, 14. 
Jan., 1883. 
Shell of medium size or larger, sub-rhomboidal, oblique; body ovate, narrow 
above; length one-fourtli 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, flat 
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,jsub-equal rays, with 
