CRETACEOUS FOSSILS. 215 



lanceolate, and deeply impressed. Surface marked by a variable 

 number of strong, concentric ribs, near the beaks, wbicb become 

 obsolete within a half or three-fourths of an inch from the apex, 

 and below which the rest of the shell is marked only by very fine 

 lines of growth. 



Figure, natural size of the largest specimen. 



Locality: Near Fort Tejon; Dr. Horn. 



By a comparison of the figure published in the Pacific R. R. Report with the 

 present one, it will he observed that there are a number of important discrepan- 

 cies. My figure is critically correct, and I can only account for the inaccuracy 

 of Mr. Conrad's by supposing that his was made from a mutilated specimen. 

 There can be no doubt but that I have identified his species, this being the only 

 shell that approaches in the most remote manner to the figure and description 

 quoted above, out of many hundreds of specimens collected at the original lo- 

 cality. The outline of the posterior end of figure 284 is restored from lines of 

 growth and from smaller specimens. 



CARDITA, Brug. 



C. VBNERIFORMIS, 11. S. 

 PL 32, Fig. 285, and 285 a. 



Shell small, very convex, subquadrate ; beaks rather large, 

 strongly incurved ; cardinal margin nearly straight ; posterior end 

 obliquely and convexly truncated; anterior end deeply excavated 

 under the beaks, produced and narrowly rounded below ; base 

 broadly rounded; lunule broad, deeply impressed. Surface 

 marked by about forty fine, acute, radiating ribs, with sometimes 

 an intercalated one arising in the middle of the shell, and be- 

 coming as large as the others before it reaches the base ; these 

 are most numerous anteriorly, where all of the ribs are smaller 

 than on the middle ; margin strongly crenulated. 



Figure 285, magnified to about three times natural size. Fig. 285 a, magnified 

 view of surface. 



Locality: "West of Martinez; Mr. Mathewson. 



