FOSSILS OF THE CARBONIFEROUS. 



241 



anterior end contracted and abruptly rounded ; basal margin broadly arcu- 

 ate and meeting the slightly oblique posterior line so as to form a rounded 

 angle ; cardinal margin nearly straight and forming an obtuse angle at its 

 union with the posterior margin. 



Surface ornamented by numerous concentric striae. 



Formation and locality. Lower portion of the Carboniferous Group, 

 northeast side of canon north of Pinto Peak, Eureka District, Nevada. 



Genus NUCULA Lamarck. 



Nucula insularis, n. sp. 

 Plate xx, fig. 14. 



Shell transverse, broadly and irregularly ovate, strongly convex, and 

 with the beaks prominent and incurved; anterior end contracted and 

 rounded somewhat abruptly, the posterior end more broadly rounded and 

 the basal line still more; the point of union of the two latter is almost 

 subangular, the posterior margin sloping upward somewhat obliquely. 



Surface marked by fine concentric striae and stronger varices of growth. 



This species is allied to N. bellastriata Conr., and N. varicosa H. and 

 W. (Pal. N. Y.,.vol. v, pt. 1, Plates and Explanations, pi. xlvi, 1883), of 

 the Hamilton Group of New York. 



Formation and locality. Lower horizon of the Carboniferous Group, 

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

 Eureka District, Nevada. 



Nucula levatiforme, n. sp. 

 Plate xxii, figs. 1, 1 a. 



Shell very small, subtriangular in outline, moderately convex. Beaks 

 elevated, incurved, situated on the anterior half of the shell. 



Surface marked by fine, strong, concentric, depressed lines of growth. 

 Interior characters unknown. 

 16 o D w 



