130 University of California Publications in Geology [ VoL - 8 



straight, longer than posterior dorsal margin, sloping more steeply 

 than the posterior dorsal margin to a narrowly rounded anterior end. 

 A narrow lunule inset in this margin is slightly concave under the 

 beaks. Ventral margin, rounded. A marked rounded umbonal slope, 

 which extends to a point between the posterior end and the ventral 

 margin, divides the shell into a posterior and an anterior part. The 

 posterior portion is a nearly flat surface while the anterior is convex. 



Dimensions. Length, 25 mm. ; height, 22 mm. ; convexity, 7 mm. 



Occurrence. Trochocyathus zitteli zone north of Mount Diablo 

 near University of California Locality 1540. 



This species is distinguished from C. grandis by its greater con- 

 vexity, by its marked umbonal slope and by lack of trigonal shape. 

 It is distinguished from C. stewartvillensis, n. sp., by its more central 

 position of beaks and by its umbonal slope. 



Named in honor of Mr. C. K. Studley. 



CRASSATELLITES STEWARTVILLENSIS, n. sp. 

 Plate 10, figure 3 



Shell large, thick, trigonal; beaks rounded, prosogyrate, approxi- 

 mate, situated a third of the distance from the anterior end. Anterior 

 end broadly rounded; posterior, rounded but narrower than anterior. 

 Posterior dorsal margin, nearly straight sloping gently to the posterior 

 end ; anterior dorsal margin, short and steep ; ventral margin, nearly 

 straight. A prominent heart-shaped lunule is set off by a rounded 

 ridge. The escutcheon is long and narrow and very definitely limited 

 by two sharp angular ridges which extend along most of its length. 

 Surface marked by growth lines only. 



Dimensions. Length of broken specimen, 28 mm. ; height, 25 mm. 



Occurrence. Found at University of California Locality 1540, 

 Trochocyathus zitteli zone, north of Mount Diablo. 



This form differs from C. grandis Gabb in the less central position 

 of the beak, in the slopes of the dorsal margins and in the less convex 

 ventral margin. It differs from C. unioides Stanton in beak position 

 and in its less elongate form. 



Named for the old coal-mining village of Stewartville, near which 

 it was found. 



