708 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



Fosition and locality. — Laramie Group. The type- specimen is from the 

 Valley of Crow Creek, Northern Colorado, 15 miles above the con- 

 fluence of that creek with South Platte Eiver. Other examples are 

 from CaSon Park, Yalley of Yampa Eiver ; Danforth Hills, near White 

 Eiver Indian agency, Colorado; and Eock Springs Station, Union Pa- 

 cific Eailroad, Wyoming. 



Volsella {Brachydontes) laticostata (sp. uov.). 



Shell transversely elongate, arcuate-subelliptical; upper border broadly 

 and almost regularly arched ; posterior border somewhat abruptly but 

 continuously rounded from the upper border to the base, which latter 

 border is gently concave along its middle portion; front abruptly 

 rounded, beaks inconspicuous, situated near the front; hinge-line short, 

 nearly straight, not forming an angle with the remainder of the upper 

 border; denticles, or crenulations of the anterior border, distinct. Sur- 

 face marked by the usual distinct lines of growth, and also by fine radi- 

 ating costse, which are obsolete along the whole length of the median 

 portion of the shell, and are more distinct upon and near the dorsal 

 border than elsewhere. 



Length 5 centimeters ; greatest width 19 millimeters. 



This species differs conspicuously from the preceding one, which is 

 from the same formation, in its greater proportionate length, the 

 straighter and less crenulate character of its costse^ and their absence 

 or obsolescence upon the median portion of the shell. 



Position and locality. — Laramie Group, about 400 feet from its base; 

 Danforth Hills, near White Eiver Indian agency^ Colorado. 



Genus NUCULANA Link. 



NuGulana inclara (sp. nov.). 



Shell small, elongate-subovate in marginal outline, gradually narrow- 

 ing behind the beaks. Beaks not prominent, situated about one-third 

 of the full length of the shell from the front; valves only moderately 

 convex, even in the anterior and umboual regions, and without distinct 

 umbonal ridges. Basal margin broadly semi -elliptical; anterior margin 

 regularly rounded from the cardinal margin to the base; postero-basal 

 margin sloping upward to the posterior margin, which is sharply 

 rounded to the cardinal margin ; the latter margin slightly arched, or 

 the anterior and posterior portions of it forming a very slight angle with 

 each other; denticles minute, numerous, 12 to 15 or more in front of the 

 beak and a greater number behind it. 



The few examples discovered being only casts, the true character of 

 the surface is not known, but it appears to have been marked with only 

 the usual concentric lines of growth. Character of the pallial line un- 

 known. 



Length 11 millimeters ; height from base to beaks 5 millimeters. No 



