1914] Dickerson: Fauna of the Martinez Eocene of California 135 



Chico contact. Elevation, 1050 feet. E. side of the NW % of Section 

 15, R. 1 E, T. 1 N, Mount Diablo Baseline and Meridian. 



MERETRIX DALLI, n. sp. 

 Plate 11, figures 2a, 25 



Shell trigonal, convex with very thin test; beaks prominent, in- 

 curved and bent forward, situated slightly in advance of the center; 

 posterior dorsal margin slightly convex and sloping steeply to the 

 rounded posterior end; anterior dorsal margin concave under the 

 beaks, rounded in advance; ventral margin gently convex; lunule 

 small; escutcheon long and very narrow; sculpture consists of fine 

 incremental lines only. 



Dimensions. Length, 22 mm. ; height, 17 mm. ; convexity, 6 mm. 



Occurrence. This species occurs abundantly in the Martinez near 

 Lower Lake. The type specimen was found at University of California 

 Locality 790. It is also found in the basal Martinez north of Mount 

 Diablo. 



M . dalli, n. sp., differs from M. stantoni, n. sp., in its much greater 

 convexity, greater height and shorter length, and the concavity of the 

 anterior dorsal margin is much greater. It differs from M. hornii 

 Gabb in shape and sculpture. M. gabbi Arnold is higher and inequi- 

 laterally trigonal, while M. dalli, n. sp., is equilaterally trigonal. M. 

 ovalis Gabb and M. uvasana Gabb have very different shapes than 

 M. dalli, n. sp. 



MERETEIX, sp. 

 Plate 11, figure 3 



Shell very convex, trigonal, beaks anterior being one-third of total 

 length from anterior end; posterior dorsal margin but slightly convex 

 and sloping to a narrow posterior end ; anterior dorsal margin, concave 

 with a well-marked, large, heart-shaped lunule, anterior end broadly 

 rounded ; ventral margin, arcuate ; sculpture, fine lines of growth only. 



Dimensions. Length, 12 mm. ; height, 10 mm. ; convexity, 3 mm. 



Occurrence. University of California Locality 1556, basal Mar- 

 tinez beds north of Mount Diablo, and University of California 

 Locality 340 southwest of Mount Diablo. 



This form, though shorter, resembles Meretrix hornii Gabb in 

 shape, but lacks its marked ribbing. It differs from M. stantoni, n. sp., 

 in its larger lunule and greater convexity. 



