116 University of California Publications. [Geology 



Dimensions : — The maximum length is 21 mm., and the great- 

 est breadth is 14 mm. 



Occurrence : — This specimen was found about two miles south 

 of Martinez, on the east side of the road reading to Walnut Creek. 

 It occurs in both the upper and lower beds. 



Solen stantoni, n. sp. 



Pl. 12, Fig. 1. 



The shell is thin, elongated and moderately convex. The 

 cardinal and basal margins are nearly parallel. The beaks are 

 anterior. The base is straight and the ends somewhat 

 rounded. The posterior end is more abruptly truncated than 

 the anterior. The surface is marked by faint concentric lines of 

 growth. Passing down from the beak to the base of the anterior 

 margin there is on each side a deep, sharp constriction which is 

 nearly at right angles to the hinge line. 



Dimensions : — The maximum length of the type specimen was 

 found to be 50 mm. The greatest width is 7 mm. 



Occurrence : — This form has been found at several localities 

 in Contra Costa County. It is most common about four miles 

 south of Martinez, on the west side of the road to Walnut Creek 

 and near the mouth of Vaca canon. As yet it has been found 

 only in the upper beds. 



Pholadomya nasuta Gabb. 



Pl. VI, Fig. 6. 



The specimen which was described in Volume I, Palaeon- 

 tology of the California State Geological Survey, is distorted, 

 and hence the drawing does not represent the normal form. In 

 the distorted specimen the beak is too high and narrow and the 

 lip slants inward from beak to base. Such is not the case in 

 normal forms which are now known from perfect specimens. 



This shell is considerably inflated, beaks moderately high, 

 broad and prominent. Anterior ends incurved and approximated. 

 The posterior end is produced and rounded. The anterior end 

 is inflated and sharply truncated. The surface is marked by 

 about fourteen strong radiating ribs, which are present only on 

 the middle of the shell. Numerous prominent concentric ribs 



