FOSSILS OF THE DEVONIAN. 



185 



Genus PLATYOSTOMA Conrad. 

 Platyostoma Hneatum Conrad. 



Platyostoma lineata Conrad, 1842. Jour. Acad. Nat. Sci. Philad., vol. viii, p. 276, pi. 



xvii, fig. 7. 



Hall, 1876. Pal. N. Y., Illustrations of Devonian Fossils, Gas- 

 teropoda, pi. ix, figs. 1-21; Idem., Pal. N. Y., vol. v, pt. 2, p. 21, 

 pi. x, figs. 1-21, 1879. 



The only differences to be noted between the Nevada shells and those 

 of this species from the Upper Helderberg and Hamilton Groups of New 

 York are, that the former average a little less in size and the surface can- 

 cellation, formed by the crossing of the revolving and concentric striae, is 

 almost obsolete; this latter feature, however, is frequently seen in speci- 

 mens from both the New York formations. 



Formation and locality. Lower Devonian of Comb's Peak, Eureka 

 District, Nevada. 



Genus EUOMPHALUS Sowerby. 



Euomphalus Eurekensis, n. sp. 

 Plate xvi, figs. 2, 2 a. 



Shell large, discoidal, lower side broadly umbilicate. Volutions four 

 or more, nearly in the same plane, varying somewhat in different individu- 

 als; barely contiguous, gradually and uniformly expanding from the apex; 

 section subcircular or transversely subovate, the diameters being as 4 to 5, 

 to the outer portion of the last volution where there is a slight angularity 

 developed on the upper, outer margin. Aperture slightly expanded, with 

 a slight sinus on the upper margin. 



Surface marked by concentric striae parallel to the margin of the aper- 

 ture. 



The largest individual observed of this species has a transverse diam- 

 eter of 80 mm , measuring across the volutions. The inner volutions have 

 been decollated or removed during the maceration of the shell, leaving 

 only the outer volution and one-half of the next preceding it, the termi- 

 nation of which rises slightly above the plane of the outer volution. A 

 specimen 55 mm across the volutions has the spire depressed to the plane of 



