FOSSILS OF THE CARBONIFEROUS. 239 
Genus MODIOLA Lamarck. 
Modiola ? Nevadensis, n.'sp. 
Plate xix, fig. 8. 
Shell thin, transversely elongate, narrow anteriorly, expanding gradu- 
ally to the greatest height at a point back of the center; anterior end 
narrow and abruptly rounded; basal margin but little curved except pos- 
teriorly; posterior end somewhat narrowly rounded, and then sloping 
obliquely upward and forward to its union with the nearly straight car- 
dinal line. Beaks small, depressed, anterior. General surface rather 
strongly convex anteriorly, and also backward along the broadly-rounded 
umbonal ridge. 
Surface with fine concentric lines of growth. 
With the single valves, and without specimens showing the hinge 
structure, the generic reference is more or less doubtful. The specimen 
illustrated has been accidentally compressed anteriorly, the basal margin 
having been pushed down and beneath its true position. 
Formation and locality—Lower portion of the Carboniferous Group, on 
the low hills south of Newark Mountain by the side of Pinto Creek, Eureka 
District, Nevada. 
Genus MODIOMORPHA Hall. 
Modiomorpha ambigua, n. sp. 
Plate xx, fig. 1. 
Shell rather below the medium size, transverse and subquadrate for- 
ward to the line of the beaks, in front of which it contracts rapidly to a 
rather narrow, rounded lobe; beaks small, and situated on the anterior 
third; hinge-line slightly arcuate; posterior end broadly rounded to the 
nearly transverse basal margin, which isa little curved towards the anterior 
lobe. 
Surface marked by faint concentric striz and a few stronger lines of 
growth. 
