78 PALEONTOLOGY OF THE EUEEKA DISTRICT. 



Mountains, Eureka District, and beneath the white quartzite at Lone Moun- 

 tain, 18 miles northwest of Eureka, Nevada. It also occurs at the same 

 horizon on Pogonip Ridge, White Pine District, Nevada. 



Modiolopsis Pogouipensis, n. sp. 

 Plate i, fig. 6 ; pi. xi, fig. 13. 



Shell quite small, ovate in outline, broadest at the posterior third; hinge- 

 line two-thirds the length of the shell posterior to the beak; posterior mar- 

 gin very oblique, slightly convex, and terminating at the somewhat sharply 

 rounded posterior extremity of the shell; basal margin slightly curved, 

 almost straight along the center; anterior end of the shell broadly rounded. 

 General surface moderately convex, most prominent along the rounded 

 posterior umbonal ridge; the beak is strong and rises a little above the 

 hinge-line ; anterior muscular scar distinct ; posterior scar unknown. 



Surface smooth or marked by broad inconspicuous lines of growth. 



Formation and localities. Same as preceding species. 



GASTEROPODA. 



Genus RAPHISTOMA Hall. 



Raphistoma Nasoni Hall. 



Plate xi, figs. 21, 21 a. 



Pleurotomaria nasoni Hall (?) 1861. Kep. Prog. Geol. Surv. Wisconsin, pain., p. 34. 

 Baphistoma (Pleurotomaria) nasoni Hall, 1862. Geol. of Wisconsin, vol. i, p. 39, fig. 2 

 Raphistoma Nasoni Whitfield, 1883. Geol. of Wisconsin, vol. iv, p. 215, pi. vi, figs. 2-3. 



The Nevada shell is a closely allied or representative species of this, 

 and in its condition as a cast it is impossible to give any good specific dif- 

 ferences between them. It might be considered a distinct form from its 

 occurring at so distant a locality and at a lower geologic horizon, but 

 these circumstances are largely negatived by the facts that well-character- 

 ized Devonian species occur in New York and Nevada and at different 

 relative horizons, as will be shown under the head of the Devonian fossils; 

 and species heretofore considered as belonging to the Trenton horizon have 

 been identified in the Pogonip limestone, e. g., Orthis testudinaria, 0. trice- 



