FOSSILS OF THE JUKASSIC PERIOD. 297 



being proportionally longer, but most notably in the angular form of the 

 ribs and interspaces, as well as in the different style of transverse orna- 

 mentation. The specimen presents much the appearance of an Eocene 

 Cardita, and closely resembles C. alticostata Conrad (C transversa Lea) of 

 the Claiborne beds in Alabama, except that it is narrower anteriorly. 



Formation and locality. — In limestone referred to the Jurassic, Shoshone 

 Springs, Augusta Mountains, Nevada. Collected by S. F. Emmons, esq. 



Genus ASTARTE Sowerby. / 



ASTARTE ? ARENOSA n. sp. / 



Plate VII, figs. 20-21. 



Compare Tancredia Warrenana Meek and Hayden, Pal. Upper Missouri, p. 96, pi. 3, 

 fig. 7. 



Shell small, the largest specimens not exceeding half an inch in length, 

 by a height about two-thirds as great; form transversely suboval, or 

 quadrangularly oval ; cardinal line arcuate, but little more than half as long 

 as the body of the shell, gradually and moderately declining posteriorly ; 

 anterior end constricted in front of the beaks, and rather sharply rounded 

 below ; basal line broadly convex ; posterior end narrow and obliquely 

 truncate, being longest below at the junction with the basal border ; beaks 

 small, incurved, moderately ventricose, and situated at about one-fourth of 

 the length from the anterior end. Valves ventricose throughout, with a per- 

 ceptible fullness along the umbonal slope, above which the shell declines 

 more rapidly to the cardinal border. Features of the hinge and muscular 

 system unknown. Surface of the shell smooth, so far as can be determined 

 from the specimens examined. 



At first, we were inclined to consider this shell as identical with Tan- 

 credia Warrenana M. (loc. cit), but on closer comparison with figures and 

 description it would seem to be distinct. At least, it is not a Tancredia, and 

 may be equally distant from Astarte; but, in the absence of all generic 

 features in the specimens beyond the external form, it is impossible to say 

 definitely to what genus it does belong. It is an abundant species in some 

 localities, the rock being literally filled with the impressions. It differs 

 specifically from the above-named shell in being less distinctly triangular 



