Vol. VII] WARING—STRATIGRAPHIC AND FAUNAL RELATIONS 95 



terior, and slightly deflected. Surface marked by a few irregu- 

 lar lines of growth." Parts of a few large specimens of this 

 species were found. Locality 7. 



Venericardia planicosta homii (Gabb) 



PI. 11, Figs. 3, 4, and 5 



Cardita homii Gabb, Pal. Gal., vol. 1, p. 174, pi. 24, fig. 157, 

 1864. 



V. planicosta Arnold & Anderson, U. S. G. S. Bull. 322, pi. 

 13, ^g. 4. 



V. planicosta Arnold, U. S. G. S. Bull. 321, pi. 9, fig. 3. 



V. planicosta Arnold & Eldridge, U. S. G. S. Bull. 309, pi. 

 25, figs. 1, la, and lb. 



V. planicosta Arnold & Anderson, U. S. G. S. Bull. 398, pi. 

 24, fig. 1. 



Shell large, thick, cordate, deeply convex; length greater 

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

 lunule large; anterior cardinal margin deeply excavated in 

 front of the beaks, slightly convex and about twice as long as 

 in V. planicosta venturcnsis; anterior margin convex and 

 flared; posterior margin convexly truncated; surface orna- 

 mented with about 22 broad, rounded ribs which become very 

 broad, and almost obsolete near the margins in the adult ; inter- 

 spaces shallow, linear; surface marked by wrinkled lines of 

 growth. Locality 8, L. S. J. U. Pal. Coll. Only sandstone 

 casts of this species were found. 



This subspecies, for so long called V. planicosta Lam. by 

 Pacific Coast geologists, certainly deserves at least subspecific 

 rank. In our California Eocene there are, no doubt, three dis- 

 tinct forms of Venericardia. The young, pi. 11, fig. 5, shows 

 the characteristic knotted ribs of the young stages of V. plani- 

 costa homii. The ribs are fine, hair-like, with deep interspaces ; 

 they are mounted by rows of tubercles until they attain a height 

 of about 14 mm., after which they are abruptly rounded. 



This subspecies is distinguished chiefly by the flaring mar- 

 gins, broad, flat ribs, linear interspaces, and by the greater 

 length as compared with the height. It grows to be much 



