178 PALEONTOLOGY OF THE BUREKA DISTRIOT. 
it was of medium width, and nearly one-half the length of the shell on the 
lower side. 
Surface marked by fine radiating strie on the body and anterior 
slope, and stronger strize or ribs on the alate posterior portion of the shell; 
traces of fine concentric striz are discernible, which under more favorable 
conditions of preservation would probably be a prominent feature. ; 
This species is allied to a form from the Schoharie grit of New York, 
but with its short ventricose body, slender posterior extension, and rounded 
umbonal angle it differs from any described Devonian species known to me. 
Formation and localities—Lower Devonian horizon of Gray’s Canon, 
and Comb’s Peak, Eureka District, Nevada. 
Genus PARACYCLAS Hall. 
Paracyclas occidentalis H. & W. 
Lueina (Paracyelas) elliptica, var. occidentalis. Hall & Whitfield, 1872. Twenty-fourth 
Ann. Rep. N. Y. State Museum Nat. Hist., p. 189. Twenty-seventh, ibid., 
: pl. xii, figs. 14-16, 1875. 
Paracyclas elliptica, var. occidentalis Hall. Pal. N. Y., vol. v, pt.1; Plates and Expla- 
nations, p. 18, pl. lxxii, figs. 31-33. 
The specific resemblance of the Nevada to the Ohio shell is so close 
that when placed in the same tray it is difficult to separate the two except 
by lithologic characters. 
It has a much greater vertical range in Nevada than in Ohio, occurring 
near the base and the summit of the Devonian, and in Ohio only at the 
Upper Helderberg horizon. 
Formation and localities —Lower Devonian of Lone Mountain; Middle 
and Upper Devonian of Rescue Hill, west of Rescue Camion, and at The 
Gate, northwest of Eureka, Nevada. 
Genus POSIDONOMYA Bronn. 
Posidonomya levis, n. sp. 
Plate iv, fig. 6. 
Shell thin, broadly truncato-ovate. General surface depressed and but 
very slightly convex towards the beak on the rounded umbonal slopes. 
