CRETACEOUS FOSSILS. 149 



C. Tkaskii, 11. S. 



PI. 22, Fig. 121, and 121 a. 



Shell small, convex; beaks large, strongly incurved. Left 

 valve most convex; anterior end produced, slightly curved; pos- 

 terior end obliquely truncated; surface closely marked by small 

 but regular and well-marked concentric ribs. Right valve flatter; 

 anterior end not so produced ; surface not so strongly striate. 



Length, .27 inch ; width, .19 inch. 



Localities: Texas Flat, Placer County; Tuscan Springs, Tehama County; ami 

 Pence's Eanch, Butte County (Division A.). 



C. CELTRIFORMIS, 11. S. 

 PI. 22, Fig. 122. 



Shell elongated, narrow ; beaks moderate, nearly central. 

 Valves nearly equal. Left valve broadly excavated in advance 

 of the beaks, convex posteriorly; anterior end produced, rounded 

 narrowly; basal margin broadly and regularly convex. Right 

 valve more deeply and abruptly excavated in front of the beaks, 

 not so convex as the left valve. Surface plain, or marked only 

 by a few faint lines of growth. 



Length, .4 inch ; width, .23 inch. 



Locality: Abundant west of Martinez (in Division A.). 



C. IIornii, n. s. 



PI. 29, Fig. 238. 



Shell rather large, broad, narrow and very convex; beaks 

 central; anterior end produced and regularly rounded : posterior 

 end obliquely truncated; cardinal margins sloping equally; basal 

 broadly and regularly convex. On the left valve a sharp, angular 

 ridge passes from the beaks to the posterior basal margin, behind 

 which the surface is concave. The right valve has nearly the 



