486 University of California Publications in Geologi) I Vol. 9 



nearly straight ; posterior dorsal slope slightly convex, limited by an 

 indistinct ridge which extends from the beak to the base of the shell ; 

 anterior extremity more sharply pointed than the posterior ; base 

 very broadly rounded, hinge plate relatively broad, chondophore 

 oblique, shallow, apically roofed by a broad flat spur ; left cardinal 

 prominent, high, arms broad, extending from the dorsal to the ventral 

 margin of the plate ; ventral sinus narrow, flat ; right cardinal with a 

 prominent anterior arm, and a well-developed, although relatively 

 thin posterior arm ; laminae long, distant from the beaks ; anterior 

 lateral formed from the margin of the plate, with top rounded, distant 

 from the anterior arm of the cardinal ; posterior lateral also with 

 rounding top, dorsal and ventral slopes nearly equal; anterior ventral 

 lamina formed from the upturned edge of the hinge plate, and not 

 confluent with the anterior cardinal arm ; anterior dorsals scarcely 

 developed, considei'ably smaller than the corresponding posterior one. 

 The general shape is quite uniform. 



This trigonal species might be mistaken for S. ashburneri (Gabb). 

 It differs from that Cretaceous species in being less ventricose ; in 

 having more pronounced concentric sculpture ; and in the possession of 

 a well-developed posterior cardinal arm. 



Type described from Parson's Peak, Fresno County, California, 

 University of California Locality No. 672. 



Occurrence. — Eocene, Tejon group, Parson's Peak, south side of 

 Mount Diablo, and Salt Creek, Fresno County, California (Dickerson). 



Dimensions. — Length, 18.6 mm. ; height, 14.2 mm. ; convexity, 4 mm. 



TIVELA PACKARDI, n. sp. 

 Plate 38, figures 2a, 2b 



Shell small, trigonal in outline; base broadly rounded; beak small, 

 prominent ; lunule inconspicuous and not definitely set off. The 

 slightly convex posterior dorsal margin is gentler than the anterior 

 dorsal margin. A rounded umbonal slope extends from the beak to a 

 point where the rounded base meets the slightly convex posterior end ; 

 anterior end sharply rounded. The shell is decorated by sharply 

 rounded lines of growth. These growth lines are few and larger upon 

 the posterior dorsal slope. The dentition is characteristic of the genus. 



Named in honor of Dr. Earl Packard. 



Dimensions. — Height, 10 mm. ; length, 12 mm. 



Occurrence. — University of California Locality 672. 



