CRETACEOUS FOSSILS. 161 



little more prominent below than above; basal margin nearly 

 straight. Surface marked only by faint lines of growth. 



Figure, natural size. 



Localities: In Division B., near Fort Tejon, where it is abundant, many fine 

 specimens having been collected by Dr. Horn. I have found a single small speci- 

 men at Clayton, near the coal-mines. 



T. Californica, n. s. 



PI. 30, Fig. 245. 



Shell small, very inequilateral ; beaks prominent, a little be- 

 hind the middle of the shell ; posterior margin abruptly trun- 

 cated obliquely from the beaks to the base ; anterior end very 

 prominent and rounded ; base slightly sinuous. Surface slightly 

 convex and marked by very fine lines of growth. 



Figure, slightly magnified. 



Localities: Marsh's, east of Mount Diablo. Also near Fort Tejon (Division B.). 



VENUS, Linn. 

 V. (Mercenaria?) varians, n. s. 



PI. 23, Fig. 140, 140 a, and 141. 



Shell thick, robust, inflated, variable in outline, subtriangu- 

 lar; length and breadth sometimes nearly equal, in other spe- 

 cimens, length a fifth greater than width ; beaks anterior, nearly 

 terminal; cardinal margin prominently convex, and sloping 

 rapidly downwards ; in advance of the beaks, the margin of tbe 

 shell is rather deeply excavated ; anterior end broadly rounded, 

 posterior narrower; basal margin broadly and regularly couvex. 

 Surface marked by coarse, irregular lines of growth. Lunule 

 variable, small, sometimes deep, sometimes nearly obsolete. 



Figures, natural size. 



Localities : Widely distributed in Division A. ; most abundant near Martinez, 

 and Pence's Banch, Butte County. 



The two figures, 140 and 140 a, are from specimens found near Martinez. 

 pal. vol. i. — 21 



