168 PALEONTOLOGY OF THE EUREKA 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—lLower Devonian of Brush and Atrypa Peaks, 
Eureka District, Nevada. 
Genus MYTILARCA 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°"; 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 Chemungensis Conrad. 
Plate iv, fig. 9. 
Inoceramus Chemungensis Conrad, 1842. Jour. Acad. Nat. Sci., Philad., vol. viii, p. 
_ 246, pl. xiii, fig. 9. 
Mytilus Chemungensis Phillips & Salter, 1848. Memoirs Geol. Surv. of Great Britain, 
vol. ii, pt. 1, p. 365, pl. 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; pl. xxxii, figs. 
8-14. Ibid., 1884. Text, p. 258. 
