82 PALAEONTOLOGY OF NEW YORK. 



The largest specimen is 33 mm. in length, 38 ram. in height, binge-line 



16 nun. 



This Bpecies 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. V. 



Crenipeitkn crenulatus. 



PLATE IX. FIGS. 6, 7. 8, 16, L6, 17 



PeeUnf crenulatus, Hall. Geolog. Surv. N. Y. : Rep. Fourth Dist., i>. 21;."). is-i:i. 



Crenipeeten crenidatux, Hall. Pal. N. V.. vol. v. pt. 1. Plates and Explanations: PI. 9, tisrs. 1; s. 15-17. 



Jan.. 1SS3. 



Shell of medium size, ovoid-orbicular, moderately oblique ; length and height 

 nearlv equal : margins regularly rounded, somewhat extended posteriorly. 



Right valve convex. Left valve depressed-convex above, and nearly Hat 

 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. (Jmbonal 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 21* mm., height 31 mm., hinge- 

 line 17 nun. A smaller specimen has a length of 26 nun., height 29 mm., 

 and himre-line 16 mm. 



