FOSSILS OF THE DEVONIAN. 



115 



Orthis impressa Hall. 

 Plate xiii, fig. 13. 



Orthis impressa Hall, 1843. Geol. Eep. Fourth District of New York, p. 268 and p. 267, 



fig. 2. 



impressa Hall, 1867. Pal. N. Y., vol. iv, p. 60, pi. viii, figs. 11-19. 

 impressa Whitfield, 1883. Geol. of Wisconsin, vol. iv, p. 326, pi. xxv, figs. 13^15. 

 Compare 0. Tulliensis Vauuxem, 1842, Geol. Rep. Third District, New York, p. 55. 



0. loicensis Hall. 1858, Geol. Surv. Iowa, vol. i, pt. 2, p. 488, pi. ii, figs. 

 4 a-i, and 0. Me. Farlanei, Meek, loc. cit., p. 114. 



In New York this species is found in the Chemung Group, and is re- 

 garded by Professor Hall as closely allied to Orthis Tulliensis, of the Tully 

 limestone, which occurs about 1,000 feet lower in the strata, no species of 

 Orthis being known in the interval. In Nevada the relative position of the 

 two forms is somewhat reversed; 0. impressa is found only at the base of 

 the Devonian, and 0. Tulliensis at the base arid near the summit, 4,000 feet 

 above. 



A comparison of the Chemung specimens from New York wfth the 

 Nevada examples shows a most perfect identity between them, while the 

 0. Tulliensis is quite as decided in its characters as in New York. Associated 

 with 0. impressa, at Lone Mountain, there is a- more convex form that is of 

 the type of 0. Tulliensis, and it may be referred to it. 



Formation and localities. Lower horizon of the Devonian limestone, 

 Comb's Peak; 2 miles east of Castle Mountain; west slope of County 

 Peak, and Lone Mountain, 18 miles northwest of Eureka, Eureka District, 

 Nevada. 



Orthis Tulliensis Vauuxem. 

 JPlateii, figs. 12, 12 a. 



Orthis tulliensis Vanuxem, 1842. Geol. Rep. Third District New York, p. 164 and fig. 



2, on p. 163. 



tulliensis Hall, 1867. Pal. N. Y., vol. iv, p. 55, pi. vii, figs. 5cu-k. 

 Compare 0. loicensis Hall, 1858. Geol. Eep. Iowa, vol. i, pt. 2, p. 488, pi. ii, figs. 4 a-/. 



The facts connected with the distribution and range of this species have 

 been mentioned in the notes of the preceding species. The specimens from 

 The Gate, northwest of Eureka, are not quite as gibbose as the majority 



