82 
PALAEONTOLOGY OF NEW YORK. 
The largest specimen is 33 mm. in length, 38 mm. in height, hinge-line 
16 mm. 
This species differs from P. crenulatus in its proportionally greater height, 
rotundity, and less obliquity. 
Although known only as a cast, it is distinctively different from other species. 
Formation and locality. In shales of the Chemung group at Rockville, Alle¬ 
ghany county, N. Y. 
Crenipecten crenulatus. 
PLATE IX, FIGS. 6, 7, 8, 15, 16, 17. 
Pecten? crenulatus. Hall. Geolog-. Surv. N. Y.: Rep. Fourth Dist., p. 265. 1843. 
Crenipecten crenulatus, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 9, figs. 6-8, 15-17. 
Jan., 1883. 
Shell of medium size, ovoid-orbicular, moderately oblique; length and height 
nearly equal; margins regularly rounded, somewhat extended posteriorly. 
Right valve convex. Left valve depressed-convex above, and nearly flat 
below. 
Hinge-line straight, length more than one-half the length of the valve, 
anterior to the middle of the shell. 
Beaks obtuse, central, inclined somewhat forward, not. rising above the 
hinge-line. Umbonal region of the right valve prominent, subtending an 
angle of about 100°. 
Ears small, triangular, subequal, limited on the right valve by the rapid 
slope of the sides of the umbo; margins slightly concave; extremities angu¬ 
lar. Byssal sinus not defined. 
Test thin; conspicuously marked with fine, concentric striae of growth, 
and obscure or nearly obsolete radii (as seen in figs. 7, 8 and 16, pi. 9). 
The concentric lines are stronger on the ears, and are sometimes cancellated 
by fine rays. 
Ligamental area narrow, crenulated by a row of minute cartilage-pits. 
A medium-sized specimen has a length of 29 mm., height 31 mm., hinge¬ 
line 17 mm. A smaller specimen has a length of 26 mm., height 29 mm., 
and hinge-line 16 mm. 
