240 PALEONTOLOGY OF THE EUREKA DISTRICT. 



There is some doubt attending the reference of this species to the genus 

 Modiomorpha, as the hinge structure and muscular impressions are unknown; 

 but in the absence of these characters the general form of the shell allies 

 it to that genus. 



Formation and locality. Lower portion of the Carboniferous Group, on 

 the east slope of a small conical hill on the east side of Secret-cafion-road 

 Canon, Eureka District, Nevada. 



Modiomorpha f desiderata, n. sp. 

 Plate xx, fig. 3. 



Shell of medium size; transverse, roughly suboval; beaks small, com- 

 pressed, and situated within the anterior third, the portion of the shell in 

 front of them contracting quite rapidly and becoming abruptly rounded in 

 front; the posterior end is broken away, but, from the direction of the 

 lines of growth, it was probably somewhat broadly rounded. The valves 

 are moderately convex and the surface marked by a few lines of growth. 



The nearest allied species appears to be Modiomorpha Hyalea Hall 

 (Pal. N. Y., vol. v, pt. 1, Plates and Explanations, pi. xli, fig. 28, 1883), from 

 the Waverly Group of Ohio. 



As with the preceding species the generic reference is doubtful; and, 

 although their generic relations are not clearly determined, it is thought 

 desirable to give specific names to the well-marked species of the class 

 to which they belong, as it is rarely well represented in the Carboniferous 

 Group in the Rocky Mountains. 



Formation and locality. Lower portion of the Carboniferous Group, on 

 the east slope of a small conical hill on the east side of Secret-cafion-road 

 Canon, Nevada. 



Modiomorpha f Fiutoensis, n. sp. 

 Plate xx, fig. 2.. 



Shell of medium size, transversely subelliptical in outline; general 

 surface moderately convex, with a rounded umbonal slope to the greatest 

 posterior extension of the valve on the lower third of the posterior margin ; 



