26 PALAEONTOLOGY OF CALIFORNIA. 



and crossed by flue concentric, subimbricated lines ; a sharp, 

 angular ridge runs from the beaks backwards, nearly parallel 

 with the cardinal edge, between which and the ridge is a flat 

 space sloping inwards; internal margin finely crenulated. 



Figure, natural size. 



Locality and position: From the Miocene, at Griswold's, Monterey County. 

 But a single specimen was found, and I have been unable to expose the hinge. 

 I have therefore not been able to determine positively the genus. 



CYRENA, Lam. 



C. Californica, n. s. 



PI. 7, Fig. 45. 



Shell very variable in outline, suboval or subquadrate, more 

 or less oblique; beaks prominent, varying in position from 

 almost median to nearly submarginal, the variation being prin- 

 cipally due to the greater or less prominence of the anterior end, 

 and the greater or less obliquity of the shell; anterior end 

 usually produced and most prominent above; posterior end more 

 or less distinctly truncated, the truncation being oblique. Sur- 

 face marked by numerous, irregularly disposed concentric lines. 

 Hinge teeth sharply prominent; hinge plate slightly expanded 

 on the ligament margin, extending a little beyond the general 

 outline of the shell. Pallial margin strongly impressed. 



Figure, natural size. 



Locality and position: Very abundant in the Pliocene, near the east end of 

 Xirker's Pass. 



This species is the most variable in outline of any fossil I have seen in Califor- 

 nia, except the oysters and similar shells. No two specimens have the same shape, 

 and by selecting a suitable series, differences enough could be found to make three 

 or four species, sufficiently distinct, on paper. The large number of specimens, 

 however, at my disposal, show conclusively that all belong to but one species. I 

 have never seen the shell from any but the above quoted locality. 



