ARNOLD — THE PALEONTOLOGY AND STRATIGRAPHY OF SAN PEDRO. 155 



Section Rnpcllnriu Fleurian. 



Shell inflated and loiindeti in front, attenuated and more compressed behind; sculpture 

 cliiclly radial; stronger anteriorly. 



Type, I'elricoia lilho/jJuic/u (RetziiLs). 



95. Petricola (Rupellaria) lamellifera Conrad. 



Venus lamellif era Con., Jour. Phil. Acad. Nat. Sci., Vol. VII, 1837, p. 257, PI. XIX, fig-. 19. 



Venenipis cordieri \ax. B, Desh., B. M. Catal. Ven., p. igr. No. i. 



Petricola cordieri Desh., Rev. Zool. Soc. Cur., 1839, p. 358; Mag. Zool., PI. XVIII. 



Rupellaria lamellifera Con., Carpenter, Proc. Zool. Soc, 1856, p. 214. Carpenter, Brit. Assn. 

 Rept., 1863, p. 641. Cooper, 7th Ann. Rept. Cal. St. Min., 1888, p. 262. Keep, 

 West Coast Shells, p. 183, fig. 156, 1892. Williamson, Proc. U. S. Nat. Mus., Vol. 

 XV, 1892, J). 1S4. 



Shell of medium size, convex, equivalve, inequilateral, thick; beaks anterior to middle, 

 marginal, not much elevated, turned slightly forward ; anterior extremity evenly rounded; posterior 

 extremity widely truncated; surface sculptured by ten or twelve lamelliform, concentric, slightly 

 reflected ribs, and rather faint radiating sulcations; lunule indistinct, sculptured; ligament rather short; 

 hinge strong, with two bifid and one single tooth in each valve; pallial sinus deep, narrow, pointed; 

 muscle-impressions distinct, oval. 



Dimensions. — Long. 26 mm.; alt. 21.5 mm.; diam. 16 mm. 



This specie.? resembles Petricola cnnlUoides, but is distinguisliable by the 

 prominent concentric lamellar frills. Like P. carditoides this shell bores in the 

 rocks; and all of the sjiecimens obtained were broken from the shale pebbles in 

 the upper San Pedro gravels of Deadman Island. 



Living. — Farallon Islands to San Diego (Cooper). 



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



Section Petricolaria Stoliczka. 

 Shell elongated, pholadiform, thin; hinge-teeth protracted, slender; pallial sinus deep. 

 Type, Petricola pholadiformis (Lanej. 



96. Petricola (Petricolaria) denticulata Soiverby. 



Petricola denticulata Sby., Thes. Conchyliorum (.?). 



Petricola pedroana Con., Pac. R. R. Rept., Vol. V, p. 324, PI. Ill, fig. 24, 1856. Gabb, Pal. Cal., 



Vol. II, p. 119, 1869. 

 Petricola denticulata Su\., Cpl-rve^htek, Brit. Assn. Rept., 1856, pp. 244, 297. 

 Cypricardia pedroana Con., Cooper, Bull. No. 4, Cal. St. Min. Bureau, 1894, p. 25. 



Shell small, elongate-oval, convex, thin; surface sculptured by fine, concentric, incremental 

 lines, and numerous, undulating, radiating ridges, which are most prominent on the anterior portion 

 of the shell; anterior end short and rounded; teeth small; pallial sinus deep. 



DimeJisions. — Long. 20 mm.; alt. 12 mm.; diam. 10 mm. 



