178 PALAEONTOLOGY OF CALIFORNIA. 



MYSIA, Leach, 1819. 



Diplodonia, Bronn, 1831. 

 ? M. polita, n. s. 



PI. 30, Fig. 256. 



Shell small, thin, subglobose; beaks between the middle and 

 anterior end ; base and sides form about three-fourths of a nearly 

 perfect circle; anterior end slightly excavated, immediately under 

 the beaks; cardinal margin variable, arched, or sometimes nearly 

 straight. Surface polished and marked by faint concentric lines 

 of growth. 



Figure, about three times the natural size. 



Locality: Not rare about Martinez; and also found at Clayton, near the coal- 

 mines (from Division B.). 



I have referred this shell to the above genus entirely from the external form, 

 not having succeeded in exposing the hinge of any of the specimens. 



ASTARTE, Sow. 



A. CONRADIANA, U. S. 

 PI. 24, Fig. 161. 



Shell moderate in size, elongate, subquadrate, compressed: 

 beaks small, overhanging the anterior end, which is sinuous and 

 not prominent; cardinal margin convex and slightly inclined 

 downwards posteriorly ; anal extremity convexly and obliquely 

 truncated ; basal margin broadly and regularly convex, most 

 prominent at or a little behind the middle. Surface ornamented 

 by small, regular, concentric ribs, which, when weathered, are 

 replaced by finer radiating lines. Lunule small, deep. 



Figure, natural size. 



Locality: Texas Flat, Placer County: collected by Dr. Trask. 



