ARNOLD — THE PALEONTOLOGY AND STRATIGRAPHY OK SAN PEDRO. 12r) 



Rare in tlio lower San Pedro series of De.adinan Island and nppcr San Pedro 

 series of San Pedro. Found also at Spanish liij^lit, San ])iei^o. 



Liring. — Straits of Fiica to San Diego (Cooper). 



Pleistocene. — San Pedro (Arnold): San Diego (Armiid). 



Pliocene. — San P>eniti) Connty (Cooper). 



AFiocene. — Ventura County (Cooper). 



♦ Family X\!. I.VOXSI 1 D.E. 



Genus Lyonsia Turton. 



Shell nearly equivalve, kft valve largest; thin, .subnacreous, close, truncated posteriorly; 

 cartilage plates oblique, covered by an oblong ossicle; pallial sinus obscure, angular. 



Lyonsia norvegica is a characteristic species. 



50. Lyonsia calif ornica Conrad. 



Lyonsia californica CoN., Journ. Phil. Acad. Sci., Vol. VII, 1837, p. 24S, PI. XIX, fig. 20. Cpr., 

 Proc. Zool. Soc, 1856, p. 210; =Z,. bracteala Gld. =Z,. w/V/V/a Gld., (y?(j'(? Carpen- 

 ter, Brit. Assn. Re])t., 1863, p. 638). Keep, West Coast Shells, p. 202, fig. 174, 1892. 

 Williamson, Proc. U. S. Nat. Mus., Vol. XV, 1892, j). 184. 



Shell of medium size, elongate-oval, truncated and narrowing slightly posteriorly, convex, 

 thin; long, slightly depressed posterior to umbo; short, convex anterior; surface sculptured with 

 fine, concentric, incremental lines; external layer chalky and fugacious, pearly beneath; cartilage- 

 plates oblique, covered by an oblong ossicle; pallial sinus obscure. 



Dimensions. — Long. 31 mm.; alt. 14 mm.; diam. 11 mm. 



This frail shell is generally found with the outer layer gone, leaving the pearly 

 surface of the lower layer exposed. Outline variable. 



Specimens identified by Dr. Dall. 



Kather common in the Pliocene of Deadman Island, the lower San Pedro 

 serie.^ of Deadman Island and San Pedro, and the upper San I'edro series of Dead- 

 man Island, Crawfish George's, and San Pedro. 



Living.- — Puget Sound to San Diego (Carpenter). 



Pleistocene. — San Pedro (Arnold). 



Pliocene. — San Pedro (Arnold). 



Genus Mytilimeria Conrad. 



Shell rounded oval, more or less ventricose, equivalve, fragile, covered by a thin caducous 

 epidermis; beaks subspiral; hinge without teeth, but formed of small linear excavations under the 

 beaks to receive the ligament, which contains a small ossicle; muscular impre.ssions small; pallial 

 impression with an obtuse sinus. 



Type, Mytilimeria nuttalli Conrad. 



