260 PALEONTOLOGY OF THE EUKEKA DISTRICT. 



arching backward in crossing the rather narrow surface defined by the sim- 

 ple carina above and below, they trend forward at about the same angle to 

 the suture as they do above from the band to the suture. 



Formation and locality. Lower portion of Lower Carboniferous lime- 

 stone, in canon directly south of a small conical hill on east side of Secret- 

 canon-road Canon, Eureka District, Nevada. 



Genus MACROCHEILUS Phillips. 



Macrocheilus, sp. f 

 Plate xxiv, fig. 8. 



The general form of this species is not unlike that of Macrocheilus 

 Altonensis Worthen (Geol. Snrv. 111., p. 593, pi. xxviii, fig. 8) of the Coal 

 Measures of Illinois. Owing to the imperfect preservation of the aperture, 

 it is impossible to make a satisfactory specific reference. 



Formation and locality. Lower portion of Lower Carboniferous lime- 

 stone, in canon directly south of a small conical hill on east side of Secret- 

 canon-road Canon, Eureka District, Nevada. 



Genus METOPTOMA Phillips. 



Metoptoma peroccidens, u. sp. 



Plate xviii, %. 16. 



Shell depressed, patelliform, rounded quadrangular or suboval in out- 

 line, the greater and less diameters being 26 mm and 20 mm ; apex subcentral, 

 with the sides sloping away uniformly to the lateral margins and not quite 

 as rapidly to the anterior and posterior margins. 



Surface marked by fine concentric lines or striae of growth and narrow 

 radiating lines of a darker color. The original color of the shell is par- 

 tially preserved, the dark radiating lines of color on the purplish-gray sur- 

 face giving it the appearance of a recent Acmsea (A. testudinalis). 



Formation and locality. Lower portion of the Carboniferous Group, 

 Richmond Mountain, Eureka District, Nevada. 



