CRETACEOUS FOSSILS. 171 



margin convex, curving rapidly downwards to meet the poste-. 

 rior end ; anterior end sinuous, prominent below ; basal margin 

 broadly and regularly convex. Surface marked by concentric 

 lines of growth, which are very regular towards the beaks. 

 Hinge stout ; lateral teeth about equal in size ; middle cardinal 

 tooth largest, robust, and grooved on the upper surface; pos- 

 terior cardinal tooth long, linear. Lunule rather large, but only 

 defined by an impressed line. 



Figures, natural size. 



Locality: In beds, either belonging to the newest Cretaceous, or possibly Ter- 

 tiary, south side of Corral Hollow ; associated with Corbula prlmorsa (supra), an 

 Oyster, and two or three other species, none of which were found sufficiently per- 

 fect to be properly characterized. I have also received specimens from Dr. Frick, 

 labelled "Contra Costa County." 



All of the specimens were more or less distorted ; so that it is possible that figure 

 151, which was taken from one of the best specimens, may not illustrate, with 

 perfect accuracy, the proper form of the species. However, the inaccuracy, at 

 the worst, cannot be very great. 



CAKDIUM, Linn. 



C. (Ljevicardium) annulatum, n. s. 



PI. 23, Fig. 152. 



Shell thin, moderate in size, cordate, convex, nearly equilate- 

 ral, length and breadth about equal; beaks large, prominent, 

 and strongly incurved and directed forwards ; anterior and pos- 

 terior ends regularly convex, the posterior a little the broadest; 

 base regular. Surface highly polished and ornamented by very 

 minute, waved lines of growth, and small dots composed of cir- 

 cular or elliptical impressed lines, arranged in radiating series ; 

 these rings are placed at variable distances, usually about a tenth 

 of an inch apart. 



Figure 152, natural size; 152 a, magnified view of a portion of the surface. 

 Locality: Curry's, south side of Mount Diablo, from a very hard gray sandstone, 

 in Division A. A single imperfect specimen, collected by Mr. Brewer. 



