1914] Dickerson: Fauna of the Martinez Eocene of California 131 



CRASSATELLITES CLAYTONENSIS, n. sp. 

 Plate 10, figures 4a, 4b 



Shell, elongate oval ; beak, prominent and located one-fourth the 

 distance from anterior end; posterior dorsal margin straight, with 

 gentle slope to posterior ; anterior dorsal margin short, concave ; 

 anterior end rounded ; posterior end, truncated. A rounded umbonal 

 slope extends to the junction of the posterior end and the arcuate 

 ventral margin. Surface marked in umbonal region by prominent, 

 rounded, concentric ribs. The specimens are imbedded in the matrix 

 so that a complete hinge cannot be exposed, but the cardinal teeth 

 appear to be those of Crassatellites. 



Dimensions. Length, 11 mm. ; height, 8.5 mm. ; convexity, 3 mm. 



Occurrence. University of California localities 1558, basal Mar- 

 tinez beds north of Mount Diablo, and 1547, Trochocyathus zitteli 

 zone near Muir Station. 



Named for the town of Clayton, near which one of the type 

 specimens was found. 



CAEDITA VENERIFOEMIS Gabb 



Geological Survey of California, Palaeontology, vol. 1, p. 215, 1864. 



" Shell small, very convex, subquadrate; beaks rather large, strongly in- 

 curved; cardinal margin nearly straight; posterior end obliquely and convexly 

 truncated; anterior end deeply excavated under the beaks, produced and nar- 

 rowly rounded below; base broadly rounded; hmule broad, deeply impressed. 

 'Surface marked by about forty fine, acute, radiating, ribs, with sometimes an 

 intercalated one arising in the middle of the shell, and becoming as large as 

 the others before it reaches the base; these are most numerous anteriorly, where 

 all of the ribs are smaller than on the middle; margin strongly crenulated. 



"Locality: West of Martinez. Martinez Group." 



This species has the same acute ribs as the young of V. planicosta, 

 and the same variations in form. Some specimens found in the basal 

 Martinez north of Mount Diablo vary from an elongate quadrate form 

 to a high form similar to the high variety of V. planicosta. 



PHACOIDES QUADKATA, n. sp. 

 Plate 10, figure 6 



Shell thin, compressed, markedly quadrate, high; beaks rounded, 

 prosogyrate; posterior dorsal margin straight, sloping moderately to 

 the straight posterior end, which is nearly parallel to altitude line; 



