Lamellibranchiata. 291 



Formation and locality. In the Chemung group at Chemung Nar- 

 rows, Chemung county, N. Y. 



Pteeinea consimilis. 



Pterinea consimilis, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : 

 PI. 15, figs. 1, 2, 8, 9, 11. Jan., 1883. 



Shell large, sub-rhomboidal, nearly orbicular; length greater than 

 the height; margins regularly curved, moderately produced on the 

 posterior end. Left valve convex above, depressed-convex below. 

 Eight valve convex on the umbo, flat or slightly concave below. 

 Hinge-line straight, length equal to or a little greater than the 

 length of the valve. Beak acute, anterior, inclined slightly for- 

 ward, not rising above the hinge. Umbonal region prominent but 

 not strongly limited, subtending more than a right angle. Ear 

 small, limited by the abrupt slope of the umbo, which becomes a 

 distinct sulcus in the right valve; margin convex (except in the 

 byssal sinus); extremity ^rounded. Byssal sinus not distinct. Wing 

 broad, triangular, undefined, much extended; margin concave ; 

 extremity acute. 



Surface of left valve marked by numerous flattened, slender, fili- 

 form rays, with broad, flat interspaces, which are marked by one or 

 two, more or less distinct, finer rays. The radii are often undulat- 

 ing, and become obscure toward the base. The cardinal expan- 

 sions are correspondingly marked. Fine, closely arranged, incon- 

 spicuous concentric strise cross the surface. The wings of both 

 valves are similar in surface characters. The body of the right 

 valve shows the concentric striae, with obscure indications of rays. 

 Ligamental area broad, marked by fine parallel grooves the entire 

 length. Lateral teeth two, strong, converging. Cardinal teeth 

 preserved as three short plications under the beak of the left valve. 

 Pallial line simple, originating anterior to the beak, continuing 

 nearly parallel to the margin of the valve, recurving and terminat- 

 ing in a large muscular scar on the post-cardinal slope adjacent to 

 the wing. 



A left valve has a length of 52 mm., height 49 mm., hinge-line 

 about 50 mm. A right valve has a' length of 46 mm., height 40 

 mm., hinge-line 48 mm. 



This species differs from P. Chemung ensis in being shorter, pro- 

 portionally more extended on the hinge-line, with wider ligamental 



