130 CALIFOHNIA AfADKMY dl' Sl'IENCES. 



Siiperfamily L I lAM Al i;.\. 



Fiiniil.v XX, CllAMlD.K. 



Genus Chama (I'lin;/) Linni. 



Shell attached ustially by the left umbo; valves loHaceous; the upper smallest; hinge-tooth 

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

 oblong, the anterior encroaching on the hinge-tooth. 



Chama lazarus Liiinr is a cliaiactciistic s]>ecies. 



57. Chama exogyra Ounrad. 



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

 PI. VII. Cari'ENTEk, Proc. Zoo!. 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, 1S92. Williamson, U. S. Nat. Mus. , 

 Vol. XV, 1892, p. 189. 



Shell of medium size, oval, irregular; left valve subcompresseil, thick, attacluti wIkii living; 

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

 foliated with irregular, disconnected, rough, translucent, concentric frills; hingc-tootii thick in free 

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

 the iiinge-tooth. 



Dimensiotis. — Long. 33 mm.; alt. 33 mm.; diani. 16 mm. 



Distinguishable ffoin 0. jicllncida by lai'ger, thicker shell, fewer and less spiny, 

 though more prominent frills; and by being attached generally by tiie 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 (Cooi)er). 



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

 Nicohis Island (Bowers). 



58. Chama pellucida Saircrhi/. 



CAama spinosa Brod. war. pel/uctda Sry., Proc. Zool. Soc, 1834, p. 150. 



Chama pellucida Siiv., Cpr., Brit. Assn. Rept., 1863, p. 641. Kekp, West Coast Shells, p. 182, 



fig. 155, 1892. Williamson, Proc. U. S. Nat. Mus., Vol. XV, 1892, 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; hinge-teeth and muscle-impressions as in C. exogyra. 



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



Distinguishable from C. exogyra by smaller size, more prominent fiills on 

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

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

 attached. Specimens identified by Dr. Dall. 



