FOSSILS OF THE CAMBEIAN. 



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 Canon, Eureka 

 District, Nevada. 



PTEROPODA. 

 Genus STENOTHECA Salter. 



Stenotheca elougata, n. sp. 

 Plato ix, figs. 2, 2 a. 



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 striae 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 Canon, Eureka District, Nevada. 



Genus HYOLITHES Eichwald. 

 Hyolithes primordialis Hall (Sp.) 



Theca primordialis Hall, 1861. Eep. Prog. Geol. Surv. Wisconsin (pam.), p. 48. 



Ibid., Geol. Wis., vol. i, p. 21, fig. 5, 1862. Ibid., Sixteenth Eep. N. Y. State 



Cab. Nat. Hist., p. 135, pi. vi, figs. 30, 31, 1863. 

 Hyolithes (Theca) primordialis Hall and Whitfield, 1873. Twenty-third Eep. N. Y. 



State Cab. Nat. Hist, p. 242, pi. ii, fig. 3. 

 Hyolithes primordialis ? White, 1874. Expl. and Surv. West 100th Merid., Prelim. Eep. 



Invert. Foss., p. 6. Ibid., vol. iv, pt. 1, p. 37, pi. 1, figs. 5a~e, 1875. 

 Hyolithes primordialis Whitfield, 1883. Geol. Wisconsin, vol. iv, p. 175, pi. 1, fig. 12. 



