80 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



sharp constriction running from it nearly perpendicular to 

 the basal margin ; surface marked by fine concentric lines of 

 growth. Loc. 4. 



The anterior end of the shell is slightly more produced than 

 Weaver's fig'ure shows. 



'fc.' 



Spisula aequilateralis, new species 

 PI. 14, Fig. 8 



Shell small, convex, equilateral, trigonal; beaks adjacent, 

 sharp, with sides sloping equally either way ; ligament sagitate ; 

 basal margin broadly curved ; surface marked by fine lines of 

 growth ; umbonal ridges sharp. Martinez formation at Loc. 

 4, L. S. J. U. Pal. Coll. 



Venericardia planicosta venturensis, new subspecies 

 PL 11, Figs. 6-9 



Shell large, thick, cordate, deeply convex, altitude greater 

 than the length ; beaks large, turned forward, nearly touching ; 

 lunule small ; anterior cardinal margin deeply excavated in 

 front of beaks, short and convex, joining the broadly convex 

 anterior margin at a slight angle; posterior cardinal margin 

 deeply grooved and broadly convex ; posterior margin con- 

 vexly truncated ; surface ornamented by 25-30 large, square 

 shouldered ribs, which are strong clear to the margins, with 

 deep squared interspaces; posterior ribs narrow and indistinct; 

 entire surface marked by wrinkled lines of growth. Locality 

 4, L. S. J. U. Pal. Coll. 



This subspecies exhibits characteristics different from any of 

 this genus previously found on the Pacific Coast. It is probably 

 characteristic of the Martinez, or lower Eocene. It resembles 

 very closely V. planicosta Harris** from the Midway of Ala- 

 bama and Georgia. 



Its chief distinguishing features are the prominent truncation 

 of the submargins, narrowness and squareness of ribs compared 

 with the later forms, and a nearly constant relation between the 

 altitude and length, the former being slightly greater. It is 



"Bull. Am. Pal. no. 4, 1896, p. 58, pi. 4, fig. 13. 



