TERTIARY FOSSILS. 35 



lations near the margin. Muscular scar large, suboval to sub- 

 quadrate. 



Figure, natural size of a small and very equilateral specimen. The largest 

 specimen found is about six inches long. 



Locality : Cerros Island, associated with Pecten Veatchii, P. Cerrosensis, and the 

 following species. Dr. J. A. Veatch. 



O. CERROSENSIS, n. B. 



PI. 11, Fig. 61. 



SHELL small, subequivalve, very oblique, strongly falcate, 

 variable in form, upper edge entire, concave ; lower margin very 

 strongly undulated, each valve bearing four or five rounded, 

 tongue-like processes, which alternate in the two valves; the 

 margin, on each valve, between these processes, is very much 

 thickened, and presents the squamose edges of successive layers 

 of growth. Surface smooth, or marked only by rather indistinct 

 lines of growth. Hinge long and very oblique, slightly curved. 

 Muscular scars small, rounded subtriangular, 



Figure, natural size. 



Locality: With the preceding species. 



TEREBRATELLA, d'Orb. 



T. WHITNEYI, n. s. 



PL 12, Fig. 62, 62 a. 



SHELL subcircular, convexity of the two valves about equal, 

 moderate. Lower valve, beak high, area narrow, high, and flat; 

 foramen large, triangular. Upper margin of upper valve nearly 

 straight, sloping slightly from the beak; margins of the shell 

 regularly rounded. Surface marked by about thirty to thirty- 

 five small, angular, radiating ribs, with angular interspaces; no 

 median sulcus. 



