FOSSILS OF THE CAMBRIAN. 23 
this shell, its small size, bilobed dorsal valve, and subcarinate ventral valve 
distinguishing it from all other described species. 
Formation and locality—Cambrian. Prospect Mountain Group, at the 
base of the Secret Canon shale, on the west side of Secret Cation, Eureka 
District, Nevada. 
PTEROPODA. 
Genus STENOTHECA Salter. 
Stenotheca elongata, n. sp. 
Plate ix, figs. 2, 2a. 
Shell small, elongate, with the apex incurved and depressed nearly 
to the margin; laterally compressed so as to form a ridge nearly the 
entire length. Aperture elongate, ovate, somewhat acutely pointed at the 
end towards which the apex curves and rounded at the opposite extremity, 
the greatest width occurring about two-thirds the distance from the narrow 
end. Surface marked by numerous fine concentric strie and lines of 
growth. 
The narrow elongate aperture, depressed apex, and fine lines of growth 
serve to distinguish this from described species of the genus. As far as yet 
known the genus Stenotheca is confined to the Cambrian fauna. 
Formation and locality—Cambrian. Prospect Mountain Group, in 
the limestone just beneath the Secret Canon shale, on the west side of 
Secret Cafion, Eureka District, Nevada. 
Genus HYOLITHES Eichwald. 
Hyolithes primordialis Hall (Sp.) 
Theca primordialis Hall, 1861. Rep. Prog. Geol. Surv. Wisconsin (pam.), p. 48. 
Ibid., Geol. Wis., vol. i, p. 21, fig. 5, 1862. Ibid., Sixteenth Rep. N. Y. State 
Cab. Nat. Hist., p. 135, pl. vi, figs. 30, 31, 1863. 
Hyolithes (Theea) primordialis Hall and Whitfield, 1873. Twenty-third Rep. N. Y. 
State Cab. Nat. Hist., p. 242, pl. ii, fig. 3. 
Hyolithes primordialis? White, 1874. Expl. and Surv. West 100th Merid., Prelim. Rep. 
Invert. Foss., p. 6. Ibid., vol. iv, pt. 1, p. 37, pl. 1, figs. ee 1875. 
Hyolithes primordialis Whitfield, 1883. Geol. Wisconsin, vol. = p. 175, pl. 1, fig. 12. 
