170 PALAEONTOLOGY OF CALIFORNIA. 



TRAPEZIUM, Miihlfeld. 



T. CAMNATUM, 11. S. 

 PL 23, Fig. 150. 



Shell subquadrate, elongate ; the length is to the breadth as 

 seven to five ; beaks anterior, nearly terminal ; anterior end con- 

 cave under the beaks, convex and prominent below; cardinal 

 margin slightly convex, nearly horizontal, uniting by a curve 

 with the posterior end, which is obliquely truncated; basal 

 margin broadly and regularly convex; a prominent, angular 

 ridge passes from the beak to the posterior basal angle ; in ad- 

 vance of this ridge the surface is gently convex; behind it, it is 

 concave, and descends rapidly to the posterior margin. Surface 

 marked only by a few minute lines of growth. Hinge slender ; 

 the teeth are all small and narrow, the most anterior two of the 

 cardinal teeth are placed almost perpendicularly. 



Figure, twice natural size. 



Locality: Division A., Texas Flat, Placer County. Rare. 

 From the cabinet of the California Academy of Natural Sciences ; collected by 

 Dr. Trask. 



CYPRINELLA, N. Gen. 



Animal unknown. Shell regular, equivalve, subcordiform. 

 Hinge with three diverging cardinal teeth, and one anterior and 

 one posterior lateral tpoth in each valve. Pallia! sinus shallow. 



This genus appears to be closely allied to Cyprina, but is suffi- 

 ciently distinguished by the presence of a second lateral tooth, as 

 large as the single one of that genus. 



C. tenuis, n. s. 



PI. 23, Fig. 151, and 151 a. 



Shell moderately large, very thin, subcordate; beaks small, 

 prominent, strongly curved inwards and forwards ; cardinal 



