80 PALAEONTOLOGY OF NEW YORK. 



Formation and localities. In the shales of the Chemung group, Angelica and 

 Philipsburg, Alleghany county, N. Y. 



Pterinopecten suborbicularis. 



PLATE VIII, FIGS. 1. ■-' ; PLATE XXIV, FIG. 10; and PLATE I. XXXII. FIG 0. 



Pterineaf suborbicularift, Hall. Geolog. Surv. N. Y. : Rep. Fourth Dist., p. 264. 1843. 

 Pterinopecten suborbUndaris, Hall. Pal. N. V., vol. v. pt. 1. Plates and Explanations: PI. 8, figs. 1, 2; 



pl. 24. fig. 10. Jan., 1883. 



Shell large, rhomboid-orbicular, slightly oblique ; length a little greater than 

 the height, or sometimes equal; pallia! margins regularly curved, less con- 

 vex on the posterior side ; post-basal margin extended. 



Left valve convex. Right valve nearly flat ; similar in general form and 

 surface markings. 



Hinge-line straight, anterior, nearly equal to the length of the shell. 



Beak obtuse, broad, rounded, somewhat depressed, directed slightly 

 forward ; a little anterior to the centre of the hinge. Umbonal region 

 expanded, subtending an obtuse angle. 



Ears triangular, unequal ; extremities angular. Posterior ear the larger, 

 undefined ; margin concave. Anterior ear limited by an obscure sulcus. 

 Byssal sinus shallow in the left valve, deep and angular in the right valve. 



Surface marked by numerous regular, rounded or sub-angular radii, which 

 increase on the left valve by intercalation, and on the right valve by bifur- 

 cation ; interspaces nearly equalling the rays. On the posterior ear the 

 rays are finer, and over the body of the shell they are strongly crenulated 

 by lamellose concentric striae. 



Internal characters unknown. The ligamental area is a simple linear 

 groove. 



A large specimen measures 63 mm. in length, 55 mm. in height, the hinge- 

 line 55 mm. Another one is 38 mm. in length, 35 mm. in height, with 

 hinge-line 35 mm. 



This species is distinguished by its sub-orbicular form, slight obliquity, nearly 

 equal Length and height, and comparatively short hinge-line. 



