LAMELLIBRANCHIATA. 241 



The specimen described is a cast of the interior, preserving the surface 

 markings in a subdued condition. The anterior margin a2:)pears to have been 

 slightly incurved and the truncation resembles that in some forms of Solen. 



Formation and locality. In the Oriskany sandstone, Schoharie, N. Y. 



Pal^eopinna recurva. 



IT.ATE XXV, FIG. li). 

 Palceophi/ia reciirva, Hali,. Pal. N. Y., vol. v, pt. 1. Plates ami Explanations: PI. 2o, %. 19. Jan., 1883. 



Shell large, elongate semi-elliptical ; axis making an angle with the hinge-line 

 of from 20°-25° ; length greater than twice the height ; basal margin very 

 broadly curving ; posterior margin rapidly rounding and recurving tow^ard 

 the beak. 



Left valve depressed-convex below, convex above and becoming gibbous 

 toward the beak. Right valve unknown. 



Hinge-line straight, not extending as far as the posterior extremity. 



Anterior end unknown. Wing not defined ; margin continuous with the 

 post-basal margin and abruptly incurving at the extremity. 



Test thin, marked by fine sub-equal striae of growth, which become 

 lamellose on the pallial margin ; and by radii of unequal strength, which are 

 are sometimes strongly crenulated by the concentric striae. Anterior to the 

 middle of the shell the radii are obscure. 



Interior unknown. 



The specimen described is imperfect on the anterior end but preserves a 

 length of 120 mm., and a height 02 mm. 



This species differs from the preceding in its larger size, broadly rounded 

 posterior extremity, and the hinge not extending as far as the posterior 

 margin ; the body is also more oblique and less convex. 



Formation and locality. In limestone of the Upper Helderberg group, 

 Stafford, Genesee county, N. Y. 

 31 



