140 CALIFORNIA ACADEMY OF SCIENCES. 



collection of Delos Arnold. Found abundantly in the Pleistocene of Twenty-sixth 

 Street and Spanish Bight, San Diego. 



Living. — Gulf of California to Panama (Dall). 



Pleistocene. — San Pedro (Cooper; Arnold): San Diego (Cooper; Dall; Arnold). 



Subgenus Cerastoderma Movch.. 



Shell rotund or obovate, closed; with strong ribs obsoletely granulosa or intricate or smooth; 

 no posterior or anterior area; channels single; hinge normal. 



Type, Cardium edule (Linne). 



73. Cardium (Cerastoderma) corbis Mariyn. 



Pectunculis corbis Mart., Univ. Conch., PI. XXVIII, fig. 2, p. 1784. 



Cardium corbis Mart., Carpenter, Brit. Assn. Rept., 1863, p. 642, ^=C. californicum Con. =C. 



7milalli Co-a. {fide Gabb, Pal. Cal., Vol. II. p. 98, 1869). Cooper, 7th Ann. Rept. Cal. 



St. Min., 1888, p. 232. Keep, West Coast Shells, p. 180, fig. 153, 1892. Dall, Trans. 



Wagner Inst. Sci., Vol. Ill, Part 5, 1900, p. 1093. 



Shell large, subtrigonal, ventricose, thick; umbones prominent, anterior to center; surface 

 ornamented with about thirty-seven prominent, regular, squarish, close-set, radiating ridges, which are 

 made more or less rugose by incremental ridges on their surface; near the posterior margin these 

 ridges become more rounded and less prominent; between the ridges are equal, deep, canal-like grooves; 

 margin crenulated; ligament short, external, prominent; each valve with one prominent cardinal 

 tooth, and two laterals, one anterior and the other posterior; muscle impressions prominent, subequal. 



Dimensions.- — Long. 71 mm.; alt. 71 mm.; diam. 57 mm. 



Distinguishable by the regular, only slightly rugose ridges. Specimens 

 identified by Dr. Dall. 



Found in the lower San Pedro series of Deadman Island and San Pedro; and 

 in the upper San Pedro series of Deadman Island, San Pedro, Los Cerritos and Crawfish 

 George's. Found also in the Pleistocene of the bath-house, Santa Barbara. 



Living. — Kodiak to Santa Barbara; Kamtschatka (Cooper). 



Pleistocene. — San Francisco; Monterey; San Pedro (Cooper): San Pedro; 

 Santa Barbara (Arnold). 



Subgenus Laevicardium Swainson. 



Shell thin, oval, closed; middle of the valves smooth or feebly radially sculptured; ends 

 with a smooth area; hinge normal, but with the anterior laterals springing from the umbonal cavity; 

 periostracum smooth. 



Type, Cnrdiuin norvegiciim (Spengler). 



