168 PALEONTOLOGY OF THI EUBEKA DISTRICT. 



The specific name is given from the character of the localities at which 

 it occurs; both Brush and Atrypa Peaks are covered with brushwood. 



Another strongly marked species of Limoptera occurs in the Lower 

 Devonian. It is much larger and more erect than the species under con- 

 sideration. Unfortunately, the material does not permit of specific deter- 

 mination. 



Formation and locality. Lower Devonian of Brush and Atrypa Peaks, 

 Eureka District, Nevada. 



Genus MYTILAKCA HalL 



Mytilarca dubia, n. sp. 

 Plate iv, fig. 5. 



General outline broadly ovate. Hinge-line short, projecting a short 

 distance beyond the contour of the body of the shell. 



Left valve unknown. The beak of the right valve is somewhat acute 

 and projects over and above the hinge line; area unknown. General sur- 

 face strongly convex. Surface of valve apparently smooth. 



Dimensions: length, 4.25 cm ; greatest breadth, 3.75"*. 



In the absence of the ligamental area and the interior of the valves, 

 this species is provisionally referred to the genus Mytilarca. In general 

 form it is related to Mytilarca (Plethomytilus) oviformis (p. 169) of the Hamil- 

 ton Group of New York. 



Formation and locality. Lower Devonian, Lone Mountain, 18 miles 

 northwest of Eureka, Nevada. 



Mytilarca Chemuiigensis Conrad. 

 Plate iv, fig. 9. 



Inoceramus Cliemungensis Conrad, 1842. Jour. Acad. Nat. Sci., PMlad., vol. viii, p. 



246, pi. xiii, fig. 9. 

 Mytilm Chemungensis Phillips & Salter, 1848. Memoirs Geol. Surv. of Great Britain, 



vol. ii, pt. 1, p. 365, pi. xx, figs. 10, 11. (This is probably a distinct species.) 

 Mytilarca Chemungensis Hall, 1870. Prelim. Notice Lam. Shells, p. 23. Ibid., 1883. 



Pal. N. Y., vol. v, pt. 1 ; Plates and Explanations, p. 11 ; pi. xxxii, 



8-14. Ibid., 1884. Text, p. 258. 



