278 Thirty-fifth Report on the State Museum. 



Crenipecten crenulatus. 



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 Explana- 

 tions : 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 ex- 

 tended 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, trian- 

 gular, subequal, limited on the right valve by the rapid slope of the 

 sides of the umbo ; margins slightly concave ; extremities angular. 

 Byssal sinus not defined. 



Test thin, conspicuously marked with fine, concentric striaa of 

 growth, and obscure or nearly obsolete radii. 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. 



All the specimens are in the condition of casts or much exfoliated, 

 and the surface markings are therefore obscure. The species was 

 originally founded upon specimens of the left valve; the right 

 valves described occur in the same association, and have been 

 identified as of the same species. 



This species differs from C. olsoletus in its proportionally greater 

 convexity and length, and the obliquity of the transverse axis. It is 

 also longer than C. amplus. 



Formation and locality. In shales of the Chemung group at Rock- 

 ville, Alleghany county, N. Y. 



Crenipecten impolitus. 



Crenipecten impolitus, Hall. Pal. N. Y., vol. v, pt. 1. Plates andExplanations: 

 PI. 9, fig. 14. Jan., 1883. 



Shell of medium size, obliquely sub-ovate ; length somewhat less 

 than the height ; anterior and basal margins regularly rounded, 



