84 PALEONTOLOGY OF THE EUEEKA DISTRICT. 



Groups of Canada, but owing to the few salient characters to notice in a 

 description, and the entire lack of illustration, it is impossible to make spe- 

 cific identifications. The most nearly related species with which I am 

 acquainted are Metoptoma Trentonensis Billings (Pal. Foss., vol. i, p. 40, fig. 

 41, 1865), and M. perovalis Whitfield (Geol. Surv. Wis., vol. iv, p. 211, pi. 

 v. figs. 13, 14, 1883), from the Trenton limestone. 



Formation and locality. Lower Silurian, near the summit of the Pogonip 

 limestone, Pogonip Ridge, Eureka District, Nevada. 



Metoptoma ? analoga, n. sp. 

 Plate i, figs. 11, 11 a. 



Shell subconical, patelliform; outline of base broadly elliptical; apex 

 elevated, subcentral, and bending slightly to one side. 



Surface marked by slightly defined undulations of growth. 



Dimensions. Base, greater diameter, 11 mm ; lesser diameter, 9 mm ; height 

 of apex above base, 6 mm . 



This somewhat irregular shell occurs at the same geologic horizon as 

 M. Phillipsi, but not in the same stratum of rock. It is a well-marked 

 species, approaching the common form of a true patella more than the forms 

 usually referred to Metoptoma. As with all generic references of the Pale- 

 ozoic patelloid shells, when the interior muscular scars are unknown, it is 

 more or less arbitrary. 



Formation and locality. Lower Silurian, near the summit of the Pogonip 

 limestone, Pogonip Ridge, Eureka District, Nevada. 



Genus CYETOLITES Conrad. 

 Cyrtolites sinuatus H. & W. 



Cyrtoliies sinuatus Hall & "W bitfield, 1877. Geol. Expl. Fortieth Par., vol. iv, p. 237, 

 pi. i, figs. 23, 24. 



The type of this species is from the Pogonip limestone of Pogonip 

 Mountain, in the White Pine Mining District, Nevada. It also occurs in 

 the upper beds of the same group at Lone Mountain, 18 miles northwest of 

 Eureka, Nevada. 



