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-cation-road 
Canon, Eureka District, Nevada. 
Modiomorpha ? 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, pl. 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-cation-road 
Canon, Nevada. 
Modiomorpha ? PintGensis, 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 uf the valve on the lower third of the posterior margin; 
