154 CALIFORNIA ACADEMY OF SCIENCES. 



Externally this species mucli resembles a Kellia, but may be distinguished by 

 the pallial sinus and hinge teeth. Specimens identified by Dr. Dall. 



Two left valves from lower San Pedro series of Deadman Island, one of which 

 is figured, and is now in the collection of Delos Arnold. Rather common in the 

 Pleistocene at Spanish Bight, San Diego. 



Living. — Vancouver Island to Todos Santos Bay (Dall). 



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



Family XXIX. PETRICOLID.E. 

 Geuus Petricola Lamarck. 



Shell oval or elongated, thin, tumid, anterior side short; hinge with generally three teeth in 

 each valve, the external often obsolete; pallial sinus deep. 



Type, Venus lapicida (Chemn.). 



Section Petricola Larnarch a. s. 



Shell ovate, with a short or moderately wide pallial sinus, the radial sculpture more or less 

 divaricate or zigzag. 



Type, Petricola lapicida (Gmel.). 



94. Petricola carditoides Conrad. 



Saxicava carditoides CoN., Jour. Acad. Nat. Sci. Phil., Vol. VII, 1837, p. 255, PI. XX, fig. 8. 



Petricola carditoides Con. , Jour. Acad. Nat. Sci. Phil., 1849, p. 213. Carpenter, Proc. Zool. Soc, 

 1856, p. 214; =/". califorjiica CoN. ^P. cylindracea Desh. =/*. arcuata Desh. ^P. 

 gibba MiDD. (7?^^ Carpenter, Brit. Assn. Rept., 1863, p. 641). Cooper, 7th Ann. 

 Rept. Cal. St. Min., 1888, p. 258. Keep, West Coast Shells, p. 183, 1892. William- 

 son, Proc. U. S. Nat. Mus., Vol. XV, 1892, p. 189. Dall, Trans. Wagner Inst. Sci., 

 Vol. Ill, Part 4, 1898, p: 835; Part 5, 1900, p. 1059. 



Shell of medium size and variable outline, generally oblong-oval, conve.x, thick; surface 

 ornamented with fine, concentric, incremental lines, which sometimes form irregular ridges, and by 

 fine, wavy, radiating lines; hinge-area prominent; three cardinal teeth in each valve, the anterior one 

 smallest; margin smooth. 



Dimensio7ts. — Long. 28 mm.; alt. 25 mm.; diam. 16 mm. 



A variable form which is recognized, however, by its sculpture, prominent 

 teeth and thick shell. Often found in holes in the pebbles and boulders comprising 

 the conglomerate in this formation. Specimens identified by Dr. Dall. 



Not uncommon in the lower San Pedro series at Deadman Island; and in 

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

 San Pedro. Found also in the Pleistocene at Spanish Bight, San Diego. 



Living. — Sitka to San Diego (Cooper). 



Pleistocene. — San Pedro to San Diego (Cooper): San Pedro; San Diego 

 (Arnold). 



