34 PALAEONTOLOGY OF CALIFORNIA. 



triangular, not deep, and sometimes slightly oblique ; inner mar 

 gin of the shell not denticulated. Muscular scar broad. 



Figures, natural size. 58 and 58 a, lower valves; 58 b, an upper valve found 

 associated with the others, and apparently belonging to the same species. 



Locality: On San Lorenzo Creek, Monterey County; either Miocene or Plio 

 cene. Collected by Mr. M. Atwood. 



This shell resembles somewhat the 0. conchaphila from the coast, but differs in 

 the style of sculpture, the shape of the hinge, and the absence of the internal den- 

 ticulations. 



O. TAYLORIANA, n. s. 



PL 12, Fig. 60, 60 a. 



SHELL large, thick, irregularly subtriangular, resembling some 

 what some of the more massive forms of 0. Virginica; not attached. 

 Surface covered by heavy, irregular, subsquamose plates, showing 

 more or less of a faint undulation on their edges. Interior un 

 known. Hinge broad and short (?). ' 



Figures, natural size. 



Locality and position : From the Miocene ; from San Marcos Pass, near Santa 

 Barbara. Collected by A. S. Taylor. 



O. YEATCHII, n. s. 



PL 11, Fig. 69. 



SHELL large, subequivalve, varying from nearly equilateral to 

 very oblique, the obliquity being always to the left side. Sur 

 face marked by ten or a dozen large, angular, radiating ribs, 

 some of which arise at or near the beaks, the others branching 

 from the first, or interpolated between them ; the interspaces are 

 angular, and the ribs are marked by more or less squamose 

 plates, and occasionally these plates assume almost the character 

 of spines; internally the ribs show only towards the margins. 

 Hinge short, very broad and shallow; no crenulations or denticu- 



