178 PALEONTOLOGY OF THE EUKEKA DISTEICT. 



it was of medium width, and nearly one-half the length of the shell on the 

 lower side. 



Surface marked by fine radiating striae on the body and anterior 

 slope, and stronger striae or ribs on the alate posterior portion of the shell ; 

 traces of fine concentric striae 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 PAEACYCLAS Hall. 

 Faracyclas occidentalis H. & W. 



Lucina (Paracyclas) elliptica, var. occidentalis. Hall & Whitfield, 1872. Twenty-fourth 

 Ann. Eep. N. Y. State Museum Nat. Hist., p. 189. Twenty-seventh, ibid., 

 pi. xii, figs. 14-16, 1875. 



Paracyclas elliptica, var. occidentalis Hall. Pal. N. Y., vol. v, pt. 1 ; Plates and Expla- 

 nations, p. 18, pi. Ixxii, 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 Canon, and at The 

 Gate, northwest of Eureka, Nevada. 



Genus POSIDONOMYA Bronn. 



Posidonomya leevis, 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. 



