72 PALEONTOLOGY OF THE EUKEKA DISTRICT. 



Genus ORTHIS Dalman. 



Orthis perveta Courad. 

 Plate xi, figs. 3, 3, b. 



Orthis perveta Conrad, 1843. Proc. Acad. Nat. Sci. Phila., vol. i, p. 333. 



Hall, 1852. Pal. New York, vol. i, p. 120, pi. xxxii, figs. 5a-c. Ibid. 



Geology of Wisconsin, p. 42, figs. 7-<Z, 1862. 

 Billings, 18G3. Geol. Canada, p. 130, figs. 57 a-f. 



This species is quite abundant in the upper beds of the Pogonip Group 

 at Lone Mountain, and it also ranges through nearly 1,000 feet of the lime- 

 stone of White Mountain, and is found at about the same horizon on the 

 eastern slope of the ridge east of the Hamburg mine, as in the lower beds of 

 White Mountain. 



A direct comparison of the Nevada specimens with the types of the 

 species in the American Museum collections show their specific identity, 

 and also that similar variations occur in examples from the widely-separated 

 localities. In Wisconsin it is found in the Trenton limestone, and in Canada 

 Mr. Billings identified it from the Chazy limestone. 



A small but quite perfect specimen is illustrated. Owing to the partial 

 exfoliation of the shell, the radiating strife are not as strong as on the unin- 

 jured surface. 



In the expedition of 1882 this species was found in the upper part of 

 the Pogonip Group, on Pogonip Ridge, White Pine District, Nevada. 



Orthis testudiiiaria, Daliuan. 

 Plate xi, figs. 10, 10 a. 



Orthis testudinaria Dalraau, 1827. Vet. Acad. Hand., Stockholm, p. 115. 



Orthis testudinaria Conrad, 1839. Emmous, 1842 ; Hall, 1852. Pal. N. Y., vol. i, p. 117 r 



pi. 32, tigs. I a-l. Whitfield, Geol. of Wisconsin, vol. iv, p. 258, pi. xii, figs. 



5. 7, 1883. 

 See Davidson's Monograph British Silurian Brachiopoda. 



After comparing our specimens with those from New York, Ohio, and 

 Wisconsin, we are unable to discover any differences of specific value be- 

 tween them, although the eastern forms are from the Trenton Groups Tren- 

 ton limestone and Hudson River formations, and the Eureka specimens 



