J 52 CALIFORNIA ACADEMY OF SCIENCES. 



Shell large, transversely elliptical, equi valve, inequilateral, convex, thick; umbones turned, 

 anterior to middle: anterior end evenly rounded; posterior end much more produced, having a slight 

 tendency toward biangulation; surface sculptured with strong, elevated concentric lines, which in the 

 adult often have the prominence of concentric lamina; ligamental area external, wide, long, strong; 

 cardinal teeth four, anterior one long and narrow; pallial sinus long, rather narrow, rounded extremity 

 near middle of shell and impressed against the posterior adductor scar. 



Dimensions. — Long. 89 mm.; alt. 62 nmi.; diam. 44 mm.; umbo to anterior extremity 

 30 mm. ; to posterior extremity 59 mm. 



Specimens identified by Dr. Dall. 



Rare in tlie lower San Pedro .series of Deadnian Island; common in the upper 

 San Pedro series at Deadman Island, Crawfish George's, Los Cerritos and San Pedro. 

 Found also in the Pleistocene at Barlow's ranch, Ventura, and at Twenty-sixth Street, 

 Ban Diego. 



LiiHiicj. — Paulines Bay to San Diego (Cooper). 



Pleistocene. — Santa Barbara to San Diego (Cooper) : San Pedro; Bhikeley, 

 near Seattle, Washington (Arnold): San Diego; Ventura (Arnold). 



Pliocene. — Kirker's Pass, Contra Costa County; Twelve Mile House, San 

 Mateo County; Santa Barbara, San Fernando (Cooper). 



Miocene. — Martinez; Walnut Creek, Contra Costa County; Santa Cruz; Santa 

 Inez, Santa Barbara County; Santa Monica (Cooper). 



8uhfu,n iljj GEMMIN.-E. 



Genus Psephis Carpenter. 



.Shell thin, rounded or quadrangular, somewhat inflated; pallial sinus small; three elongated, 

 thin, cardinal teeth in each valve. 



Psejjhis lordl (Baird) is a characteristic species. 



91. Psephis salmonea Carpenter. 



Psephis salmonea Cpr., Brit. Assn. Rept., 1863, p. 641. Cooper, 7th Ann. Rept. Cal. St. Min., 

 1888, p. 261. 



Shell very small, ovate trigonal, inequilateral; posterior end evenly rounded; posterior 

 dorsal margin rounded; in other ways resembles P. tantilla. 



Dimensions. — Long. 5 mm.; alt. 4 mm.; diam. 2.5 mm. 



Distinguishable from P. tantilla by smaller size and less trigonal outline. 

 Specimens examined showed no coloration. 



Rare in the lower San Pedro series at Deadman Island and San Pedro. 

 I'^oiiiid also in liie Pliocene at Packard's Hill, and in the Pleistocene at the bath- 

 house, Santa Barbara. 



Livinr/. — Catalina Island (Cooper; Arnold): 10 fathoms (Arnold, 1901). 



Pleistocene. — Santa Barbara (Cooper): San Pedro; Santa Barbara (Arnold). 



Pliocene. — Santa Barbara (Arnold). 



