ARNOLD — THE PALEONTOLOGY AND STEATIGRAPHY OF SAN I'EDKO. 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. sitbdiaphana. 

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



This variety is very distinct from the typical C. diaphann, being much narrower, 

 less vciitricose 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 Pedro series of Dead- 

 man Island. 



Pleistocene. — San Pedro (Arnold). 



Subgenus Amiantis Carpenter. 

 Fulcra very thick and surface very concentrically rugose. 

 Type, Cytherea callosa Conrad. 



81. Callista (Amiantis) callosa Conrad. 



Cytherea callosa Co-ii.,]owr. Phil. Acad. Sci., Vol. VII, 1837, p. 252. 



Vemis callosa Con., Sowerbv, Thes. Conch., Vol, II, p. 712, PI. CXIV, figs. 44, 45. 



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



Amiantis callosa Qot^., Carpenter, Brit. Assn. Rept., 1863, p. 640. Gabb., Pal. Cal., Vol. II, 



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



St. Min., i888, p. 266. Keep, West Coast Shells, p. 187, fig. 160, 1892. Cooper, 



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

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

 Callista (Amiantis) callosa Con.; =Dione ?iobilis Rve. {Jide 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. 



Dimensio7is. — Long. 66 mm.; alt. 55 nmi.; diam. 34 mm.; umbo to anterior extremity 

 20 mm.; to pgsterior extremity 46 mm. 



Cooper (Seventh Ann. Rept. Cal. St. Min., p. 266) says that this species is like 

 Ta^es montana, described by Conrad from the " I\[iocene 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 31, 1902. 



