200 PALAEONTOLOGY OF CALIFORNIA. 



margin is, however, somewhat variable, being sometimes sinuous, 

 and in other specimens concave below, so that the extremity is 

 turned up. Surface highly polished, and marked by very faint 

 lines, slightly undulated in the middle, running subparallel with 

 the base, the lower four or five running to the margin of the 

 shell before reaching the posterior angle. The substance of the 

 shell is translucent in all of the specimens. 



Figure, nearly three times natural size. 

 Locality: Cow Creek, Shasta County. 



LIMOPSIS, Sassi. 



L. TRANSVERSA, U. S. 

 PI. 26, Fig. 186. 



Shell oblique, rounded, subquadrate, widest near the posterior 

 end, which is broadly rounded ; anterior end produced, convex ; 

 base straight or slightly sinuous; beaks anterior, subterminal, 

 small, approximate; area obliquely triangular, small, divided into 

 three unequal portions by two radiating ridges. Hinge curved, 

 edentate in the middle, and with small oblique teeth at each end. 

 Surface most convex in a line running from the beaks to the 

 posterior basal region; marked by fine radiating lines, sometimes 

 obsolete, crossed by concentric lines of growth. 



Figure, slightly magnified. 



Locality: Texas Flat, Placer County; collection of the California Academy of 

 Natural Sciences, 



PECTEN, Brug. 

 P. Traskii, n. s. 



PL 26, Fig. 187, and 187 a. 



Shell compressed, elongate, outline of the lower half forming 

 two-thirds of a circle ; margins of the body, above the curve, 



