146 STUDIES IN GEOLOGY, No. 3 



Gabb, from the California Eocene, but has more inclined 

 and more anterior beaks, with finer sculpture, and is normal- 

 ly a larger species. 163 

 Variegated. Quebrada Tusillal. 



Subfamily 



Genus AMIANTIS Carpenter 



Amwntis incrassata var. ovoidalis Sacco 



PLATE IX Fig. 5. 



Amiantis incrassata var. ovoidalis Sacco, Piemonte, parte 28, p. 

 21, pi. 4, fig. 33, 1900. 



"Testa affmis var. Suessi, sed postice productior, oblon- 

 gior, subovata." Sacco, 1900. 



The shell is medium-sized, ovate, strong, inflated. Anterior 

 margin bluntly angulate at its extremity ; ventral margin 

 broadly arcuate ; curve of posterior angle rather broad. 

 Umbones strongly prosogyrate, the points twisted back 

 about 1.5 mm. from the hinge, inclined forward, full, 

 rounded above, somewhat distant. Surface evenly convex, 

 the valves joining ventrally at an angle somewhat more 

 acute than that of most specimens of A. incrassata s.s. 

 Sculpture of concentric growth-lines. Escutcheon long, 

 narrow, deeply impressed, the ligament occupying the im- 

 pressed cavity which is almost closed over above by the 

 overhanging dorsal margin ; the walls of the impressed area 

 continue anteriorly to form the inner surfaces of the beaks, 

 between which the slit continues. Lunule indistinct on the 

 specimen studied, but probably similar to that of incrassata f 

 i.e., large, bounded by a somewhat faintly impressed line. 

 Hinge normal to the genus. Inner shell smooth ; there is no 

 evidence of radial ribs on the inner disk. Length, 44 ; height, 

 41.5; diameter, 30.5 mm. 



163 Pal. Cal., p. 169, pi. 32, fig. 282, 1864; Dickerspn, Proc. Cal. Ac. 

 Sc., 4th ser., vol. 5, p. 82, pi. 3, figs, i, a, b, c, 1915. 



