82 PALEONTOLOGY OF NEW YORK. 



Tlie larjjest speoimtMi is 88 mm. in lon,t;:th, 88 mm. in liciirht, liiiiL'^c-line 

 IG mm. 



Thi.s species differs from P. crenulalus in its pn)]i()rti(>n:illy irrentcr licinlit, 

 rotiuulitv, and less ol)iiquity. 



Altliouffh known o\\\y as a cast, it is distinctivL'ly different iVoin otlicr s])ecies. 



Formation and locality. In shales oi" tlie Cliemunj; group at luH'.k\ ille, AUe- 

 jrliany county, N. Y. 



Crenipkcten CRENULATUS. 



IT. ATE IX, KKJS. fi. 7. s, 15, Hi, 17 



I'nltn! crenntai ii.<i, H.M.L. (tCoIo^-. Surv. N. Y. : Rep. Fourth Dist., p. 21)5. 1S43. 



Crenipet-tfii in-Kiiidatiut, Hai.l. Pal. N. Y., vol. v, pt. ]. Plate.s and Explanation.* : PI. SI, tip;. tj-S. ).")-17. 



Jan., 1883. 



Shell of medium size, ovoid-orhicular, moderately oblique ; length and liciulit 

 nearly equal; margins regularly rounded, somewhat extended posteriorly. 



Right valve convex. Left valve depressed-convex ahove. and nearly Hat 

 below. 



Hinge-line straight, length more than one-half the length of the valve, 

 anterior to the middle of the sliell. 



Beaks obtuse, central, inclined .somewhat foi-ward. not I'ising aliove the 

 hinge-line. Unibonal region of the right valve ]ii()inincnt, siilitending 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. Ryssal sinus not defined. 



Test thin; conspicuously marked with fine, concentric striae of growth. 

 and obscure or nearly obsolete radii (as seen m figs. 7, 8 and 16, pi. '.)). 

 The concentric lines are stronger on the ears, and are sometimes cancellated 

 by fine rays. 



Ligamental area narrow, creiudated l)y a row of iiiiiiute cartilage-pits. 



A medium-sized speciuien has a length of 'JU mm., height 81 iiiiii.. hinge- 

 line 17 mm. A smaller specimen has a length of lii'i nnii., height 29 mm., 

 and binge-line 16 mm. 



