276 Thirty-fifth Beport osr the State Museum. 



Surface marked by closely arranged, rounded or sub-angular rays, 

 which increase by intercalation and bifurcation. The ears are 

 marked by simple and smaller rays, which in the right valve are 

 distinctly angular. The rays become obsolete on the umbo. The 

 concentric striae are close, undulating, and in some conditions may 

 have been sharply elevated and lamellose. 



A specimen is 55 mm. in length, 46 mm. in height, hinge-line 38 

 mm. 



The comparison of this species with P. crenicostatus is given 

 under the description of that species. In surface ornamentation 

 this species somewhat resembles P. Vertumnus, but the shell is 

 shorter and less oblique, the hinge-line shorter, and the concentric 

 striae less elevated . 



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

 Angelica and Philipsburg, Alleghany county, N. Y. 



Pterinopectek suborbicularis. 



Pterinea? suborbicularis, Hall. Geolog. Surv. N.Y.: Rep. Fourth Disk, p. 264. 

 1848. 



Pterinopecten suborbicularis, Hall. Pal. N.' Y., vol. v, pt. 1. Plates and Ex- 

 planations : PL 8, figs. 1, 2 ; pi. 24, fig. 10. Jan., 1883. 



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

 greater than the height, or sometimes equal ; pallial margins regu- 

 larly curved, less convex on the posterior side ; post-basal margin 

 extended. Left valve convex. Eight 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 center 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 bifurcation ; interspaces nearly equaling 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. 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. 



