194 CALIFORNIA ACADEMY OF SCIENCES [Proc. 30 Ser. 



the usual size is }^ of an incli. The disk is thin and flattened but shows a 

 decided tendency to form elevated stars on the upper surface. 



Occurrence. — This form is extremely abundant locally in 

 the Temblor Beds of the Mount Diablo Range, at Tar 

 Springs, Kreyenhagen's, and Temblor. 



Cassidulus californicus n. sp. 

 Plate XIII, Figs. 6 and 7. 



Test small, elliptical, robust and often somewhat globular; lower surface 

 flattened, or concave, upper surface convex; mouth not central, round, and 

 occupying a position ^-^ of the distance from the anal margin; anal pore ter- 

 minal; apical star nearly symmetrical, central on dorsal surface; tubercula- 

 tion distinct, the tubercules lying within rounded pits. There is a tendency 

 to form shoulder-like expansions on the periphery behind the position of the 

 mouth. 



Ocairrence. — This species is not rare in the Avenal Sands 

 west of Coalinga. 



LAMELLIBRANCHIATA. 



Eocene. 



Spondylus carlosensis n. sp. 



Plate XIII, Fig. i. 



Shell of medium size, sub-circular or obliquely ovate, radially ribbed, 

 convex; costae granulated or obscurely spinose; ears and hinge rather 

 broad. The costae radiate in graceful, sinuous lines from the beak to the 

 margins, and occur in pairs or triplets, every second or third rib being inore 

 elevated than the others. 



Occurrence. — This species occurs only rarely in the Avenal 

 Sands west and north of Coalintja. 



&' 



Ostrea aviculiformis n. sp. 



Plate XIII, Figs. 3-5. 



Shell small, very inequivalve, quadrate, oblique, laminated; inferior 

 valve convex and strongly arched; superior valve thin, often concave, and 

 sharply laminated in thin concentric folds; hinge broad and somewhat 



