130 CALIFOKNIA ACADEMY OF SCIENCES. 



Superfamily CHAM ACE A. 



Family XX. OHAMIDiE. 



Genus Chama {Plinu) Linnc. 



Shell attached usually by the left umbo; valves foliaceous; the upper smallest; hinge-tooth 

 of free valve thick, curved, received between two teeth in the other; adductor impressions large; 

 oblong, the anterior encroaching on the hinge-tooth. 



Chama lazarus Linne is a characteristic species. 



57. Chama exogyra Conrad. 



C/iama exogyra Con., Jour. Phil. Acad. Sci., Vol. VII, 1837, p. 256. Reeve, Conch. Icon., sp. 38, 

 PI. VII. Carpenter, Proc. Zool. Soc, 1856, p. 217; Brit. Assn. Rept., 1863, p. 641. 

 Cooper, 7th Ann. Rept. Cal. St. Min., 1888, p. 233; Bull. Cal. St. Min. Bureau, No. 4, 

 1894, p. 24. Keep, West Coast Shells, p. 182, 1892. Williamson, U. S. Nat. Mus. , 

 Vol. XV, 1892, p. 189. 



Shell of medium size, oval, irregular; left valve subcompressed, thick, attached when living; 

 umbo small, submarginal, much twisted, either dextral or sinistral, generally the former; surface 

 foliated with irregular, disconnected, rough, translucent, concentric frills; hinge-tooth thick in free 

 valve; two teeth in attached valve; adductor impressions large, oblong, the anterior encroaching on 

 the hinge-tooth. 



Dimensions.- — Long. 33 mm.; alt. 33 mm.; diam. 16 mm. 



Distinguishable from C. 'pellucida by larger, thicker shell, fewer and less spiny, 

 though more prominent frills; and by being attached generally by the left valve. 

 Specimens identified by Dr. Dall. 



Rare in upper San Pedro series of San Pedro and Los Cerritos. 



Living. — Bodega Bay to San Diego; Mexico (Cooper). 



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

 Nicolas Island (Bowers). 



58. Chama pellucida Sowerby. 



Chiuna spinosa Brod. \2.r. pellucida Sby., Proc. Zool. Soc, 1834, p. 150. 



Chama pellucida Sby., Cpr., Brit. Assn. Rept., 1863, p. 641. Keep, West Coast Shells, p. 182, 



fig. 155, 1892. Williamson, Proc. U. S. Nat. Mus., Vol. XV, 1S92, p. 189. Cooper, 



Bull. Cal. St. Min. Bureau, No. 4, 1894, p. 24. 



Shell of medium size; right valve (attached), exceedingly ventricose, rather thin; left valve 

 nearly flat, thicker; surface of attached valve sculptured with numerous prominent, spiny frills; surface 

 of upper valve with more numerous, small frills, which are sometimes spiny near the margin of the 

 valve; hingc-tccth and muscle-impressions as in C. exogyra. 



Dimensions. — Long. 20 mm.; alt. 25 mm.; diam. 15 mm. 



Distiugui-shable from G. exogxjra by smaller size, more i)rominent frills on 

 upper valve, and by the fact that in C pellucida the right valve is generally attached, 

 and is exceedingly ventricose, while in 0. exogyra the left valve is the larger, and is 

 attached. Specimens identified by Dr. Dall. 



