206 PALEONTOLOGY OF THE EUREKA DISTRICT. 



In the collections from the White Pine District, this species is found 

 in the Upper Devonian of Telegraph Peak. The specimens all belong to 

 the smaller variety in which the double sinus is almost obsolete. 



Genus LEPERDITIA Roualt. 



Leperditia rotundata, n. sp. 

 Plate xvi, fig. 5. 



Carapace of medium size, 5 mm in length by 3.5 mm in breadth; convex, 

 subovate in outline, with the anterior extremity a little narrower than the 

 posterior; dorsal margin straight, about five-sixths the length of the valves; 

 it terminates anteriorly and posteriorly in simple or slightly produced 

 angles formed by its union with the anterior and posterior margins respect- 

 ively; anterior and posterior margins broadly rounded; ventral margin 

 regularly curved and on the right valve turned under, forming a rounded 

 ventral edge to the carapace; ventral valve proportionally narrower than 

 the right, and terminating in a plain edge on the ventral margin. 



The uniform convexity of the surface is broken on the anterior and 

 posterior dorsal angles by a slight groove just within the margin, and on 

 the anterior dorsal region by a faintly-defined sulcus, indicating the position 

 of the depressed eye-tubercle ; muscular scar a little posterior to the center 

 of the valve, as shown, on a large right valve, by its having a lighter color 

 than the carapace. 



Surface smooth to the e'ye, but minutely punctate under a strong 

 magnifying glass. 



Formation and locality. Lower horizon of the Devonian limestone; 

 southeast of Richmond Mountain, Eureka District, Nevada. 



