ARNOLD — THE PALEONTOLOGY AND STRATIGRAPHY OF SAN PEDRO. 155 



Section Rupellaria Fleurian. 



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

 chiefly radial ; stronger anteriorly. 



Type, Petricola lithophaga (Retzius). 



95. Petricola (Rupellaria) lamellifera Conrad. 



Veyms lamellifera Con., Jour. Phil. Acad. Nat. Sci., Vol. VII, 1837, p. 257, PI. XIX, fig. 19. 



Veneriipis cordieri v^r. B, Desh., B. M. Catal. Ven., p. 191, No. i. 



Petricola cordieri D^sn., Rev. Zool. Soc. Cur., 1839, p. 358; Mag. Zool., PI. XVIII. 



Rtipellaria 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. 1S3, fig. 156, 1892. Williamson, Proc. U. S. Nat. Mus., Vol. 

 XV, 1892, p. 184. 



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 species resembles Petricola carditoides, but is distinguishable by the 

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

 rocks; and all of the specimens 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 (Lane). 



96. Petricola (Petricolaria) denticulata Sowerby. 



Petricola detiiiculata 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 Sby., Carpenter, 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 deepi 



Dimetisiotis. — Long. 20 mm.; alt. X2 mm.; diam. 10 mm. 



