CRETACEOUS FOSSILS. 271 



points, the lower a little the longest. Adjoining the hinge line, 

 both in advance of and behind the beaks, the surface is concavely 

 truncated, making two plain areas with converging sides, bordered 

 by sharp angles, corresponding in advance to a Innule, and pos 

 teriorly to the corselet of a Trigonia. A strongly marked umbonal 

 ridge runs from the beaks to the posterior basal angle, above 

 which the surface is concave, and in front of which it is very 

 slightly convex. Surface marked by very irregular concentric 

 ridges, less distinct towards the base, and corresponding in direc 

 tion with the lines of growth. 



Length (restored), 2.5 inches ; width, 1.3 inch ; diameter of two valves, .65 inch. 



CUCULLuEA, Lam. 



C. LNERMIS, n. 8. 

 PI. 36, Fig. 18. 



SHELL large, thick, subquadrate, very convex, variable in out 

 line. Beaks large, incurved, distant, variable in position, placed 

 sometimes but slightly in advance of the middle, sometimes not 

 more than a third of the length from the anterior end. Anterior 

 end nearly straight above, rounding into the base below; pos 

 terior end very variable, more or less produced, sloping above, 

 narrowly rounded below ; base nearly straight or slightly convex; 

 area broad, from two-thirds to three-fourths of the length of the 

 shell ; umboual ridge rounded, posterior to which the surface is 

 nearly flat, and almost at a right angle to the portion in advance. 

 Surface marked only by lines of growth ; in one unusually perfect 

 specimen, minute radiating lines can be detected near the beaks, 

 by the aid of a glass. 



Dimensions of three specimens: length, 3.0 inches; width, 2.2 inches ; diameter 

 of two valves, 2.0 inches. Length, 2.5 inches ; width, 2.1 inches; diameter of two 

 valves, 2.0 inches. Length, 1.9 inch ; width, 1.5 inch ; diameter of two valves, 

 1.3 inch. 



This shell is not unlike C. truncata, of the California rocks, hut is easily dis- 



