AKNOLD — THE PALF.ONTOLOC.Y AND STKATIGl!ArHY OF SAN PEDRO. 121 



Pleistocene. — San Pedro (Cooper, Arnold): San Diego (Arnold). 



Pliocene. — Santa Rosa; Twelve Mile House, San Mateo County; Soquel, Santa 

 Cruz Count}'; San Fernando; San Dies^o well (Cooper): San Diego (Arnold). 



Miocene. — El Toro Ranch, ^ronterey County; Foxin's, Santa Barbara County 

 (Cooper). 



Guuus Lithophaga Bulfen. 



Sliell cylindrical, inflated in front, wedge-shaped behind; epidermis thick and dark; interior 

 nacreous. 



Type, Mytilus liihophagns Linne. 



44. Lithophaga plumula Hanley. 



Lithopkagus phnmtla Hanley, Carpentek, Brit. Assn. Rept., 1863,0. 644. Keep, West Coast 



Shells, p. 171, 1892. WiLi.iAM.soN, Proc. U. S. Nat. Mus., Vol. XV, 1892, p. 192. 

 Lithophaga plumula Hanley, Dall, Trans. Wagner Inst. Sci., Vol. Ill, Part. 4, 1S98, p. 799. 



Shell subcylindric, with nearly terminal beaks; two radial sulci extending backward from 

 the beaks, incrustation plume-like, arranged in a distinct pattern on the areas between the sulci, and, 

 when projecting beyond the ends of the valve, apposited symmetrically. 



One perfect cast of a «liell of this species was found on the inside of a Meti& 

 alia in the upper San Pedro series at Los Cerritos. 



Living. — Monterey to San Diego (Carpenter). 



Pleistocene. — San Pedro (Arnold). 



Order ANOMALODESMACEA. 



Superfamily ANATINACEA. 



Family .Kill. PERIPLOMID.E. 



Genus Periploma Schumacher. 



Shell oval, very inequivalve, inequilateral, slightly nacreous ; left valve deepest ; posterior 

 side very short and contracted; hinge with a narrow, oblique, spoon-shaped process in each valve, 

 and a small triangular ossicle; an internal rib proceeds from under the hinge to the posterior margin; 

 muscular impressions unequal, the anterior long and narrow, the posterior small, semilunar; pallial 

 impression marginal. 



Periploma incequivalvis Schum. is a characteristic species. 



45. Periploma argentaria (Jonrad. 



Periploma argentaria Con., Journ. Phil. Acad. Sci.. Vol. VII, 1837, P- 238, PI- XVIII, fig. 8. 

 Carpenter, Proc. Zool. Soc, 1856, p. 211; Brit. Assn. Rept., 1863, p. 638. Cooper, 

 7th Ann. Rept. Cal. St. Min., 1888, p. 258. Keep, West Coast Shells, p. 204, 

 fig. 175, 1892. Dall, mss., 1900. 



, , . , December 27, 1U02. 



