ARNOLD — THE PALEONTOLOGY AND STKATKillAl'llY OF SAN PEDllO. 145' 



caused by a slight, very oblique truncation across the middle of the extremity; posterior portion of 

 the ventral line nearly straight; interior the same as in C. subdiaphana. 

 Dimensions. — Long. 32.5 mm.; alt. 24 mm.; diam. 15 mm. 



This variety is very distinct from tlie typical G. dia-pliana, being much narrower, 

 less ventricose and smaller; and having a shorter, more rounded anterior extremity, 

 a biangular posterior extremity, and a nearly straight ventral margin. 



This variety has been found only in the lower San I'edro series of Dead- 

 man Island. 



Pleistocene. — San Pedro (Arnold). 



Subgenus Amiantis Carpenter. 

 Fulcra very thick and surface very concentrically rugose. 

 Type, Cijtherea callosa Conrad. 



81. Callista (Amiantis) callosa Conrad. 



Cylherea callosa Coti., ]o\iv. Phil. Acad. Sci., Vol. VII, 1837, p. 252. 



Venus callosa Con., Sowerby, Thes. Conch., Vol, II, p. 712, PI. CXIV, figs. 44, 45. 



Dosinia callosa Con., Carpenter, Proc. Zool. Soc, 1856, p. 216. 



Amianlis callosa Coa., C.\rpenter, Brit. Assn. Rept., 1863, p. 640. Gabb., Pal. Cal., Vol. II, 



p. 96, 1869. Tryon, Syst. Conch., Vol. Ill, p. 178, 1884. . Cooper, 7th Ann. Rept. Cal. 



St. Min., 1888, p. 266. Keep, West Coast Shells, p. 187, fig. 160, 1892. Cooper, 



Bull. No. 7, 1894, Cal. St. Min. Bureau, p. 24. 

 Mereirix callosa Con., Fischer, Conchologie, p. 1079, 1887. 

 Callisla (Amiantis) callosa CoN.; =Dione nobilis Rye. (fide Dall, Proc. U. S. Nat. Mus. , Vol. XV, 



1892, p. 187). 



Shell large, suboval, inequilateral, equivalve, heavy; umbones anterior to center, prominent, 

 recurved; anterior dorsal margin slightly concave; anterior extremity quite sharply rounded near 

 upper margin; ventral margin evenly arcuate; posterior dorsal margin slightly arcuate; posterior 

 extremity faintly biangular; surface sculptured by numerous prominent, flat-topped, concentric 

 ridges, between which are interspaces equal in width to the ridges; lunule distinct, concentrically 

 striated; hinge heavy; two prominent, strong cardinal teeth; pallial sinus wide, deep and rather 

 pointed. 



Dimensions. — Long. 66 mm.; alt. 55 mm.; diam. 34 mm.; umbo to anterior extremity 

 20 mm.; to posterior extremity 46 mm. 



Cooper (Seventh Ann. Rept. Cal. St. Min., p. 26G) says that this species is like 

 Tapes moniana, described by Conrad from the "Miocene of San Buenaventura." 

 Specimens identified by Dr. Dall. 



Common in the upper San Pedro series of Los Cerritos, but exceedingly rare in 

 the same horizon of San Pedro. This species is very abundant in the Pleistocene at 

 Spanish Bight, San Diego. 



Living. — Santa Barbara to Lower California (Carpenter). 



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



( 19 ) December al, 1902, 



