FOSSILS OF THE CAEBONIFEEOCTS. 



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 MODIOMOBPHA 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 is a little curved towards the anterior 

 lobe. 



Surface marked by faint concentric strise and a few stronger lines of 

 growth. 



