Lamellibranchiata. 295 



yond the margin of the valve. Beak low, obtuse, inclined forward, 

 situated on the anterior third of the hinge-line. Cardinal expan- 

 sions unequal, triangular, flat ; margins concave ; extremities 

 mucronate. Ear limited by a broad, shallow sulcus extending from 

 the beak to the rounded byssal sinus. Wing large, undefined. 



Surface of both valves marked by about twenty-five strong, 

 rounded, equal rays, reaching from the umbo to the base, with 

 broad, flat interspaces which occasionally show a single fine inter- 

 mediate ray. The same surface characters extend over both cardi- 

 nal expansions. The entire surface is marked by fine, regular, sharp, 

 continuous, concentric striae. 



A left valve has a length of 44 mm., height 31 mm., hinge-line 

 49 mm. A large right valve has a height of 45 mm., length 65 

 mm., and hinge-line about 65 mm. 



This species resembles P. reversa, but differs in its comparatively 

 greater obliquity, more extended hinge, and proportionally greater 

 length. It differs from P. prora in the flatness of the left valve, the 

 strong rays, the sharp elevated striae, and the convexity of the right 

 valve. 



Formation and locality. In the Chemung group at Buck's quarry, 

 near Elmira, Chemung county, N. Y. 



Pterinea (Vertumnia) reproba. 



Pterinea ( Vertumnia) reproba, Hall. Pal. N. Y., vol. v, pt. 1. Unpublished. 



Shell of medium size, rhomboidal ; body oblique ; length somewhat 

 greater than the height ; pallial margin regularly rounded, becom- 

 ing produced behind and extending thence in a nearly direct line 

 to the hinge . Valves depresse,d-convex, the right valve the more 

 convex ; very similar in form and surface markings. Hinge-line 

 straight, length greater than the greatest length of the shell, ex- 

 tended- anteriorly considerably beyond the margin of the valve. 

 Beaks obtuse, not prominent, directed forward, anterior to the mid- 

 dle. Umbonal region undefined. Ear defined by a shallow sulcus ; 

 margin concave ; extremity acute. Byssal sinus moderate, marked 

 in the right valve by a partial reflexion of the margin. Wing large, 

 triangular and undefined ; margin nearly straight below, slightly 

 concave toward the extremity, which is acute. 



Surface marked by numerous strong, rounded rays, which alternate 

 on the left valve, and duplicate on the right valve. The interspaces 

 are equal to, or greater than, the radii; the rays are finer on the 



