FOSSILS OF THE CAEBON1FEROUS. 



Genus RHYNCHONELLA Fischer. 



223 



Rhynchonella Eurekensis, n.Jsp. 

 Plate xviii, figs. 8, 8a-c. 



Shell below the average size; somewhat trigonal in outline; the width 

 and height subequal, or the latter a little greater than the former; dorsal 

 valve a trifle deeper than the ventral. 



Ventral valve with a prominent beak and strongly marked but not 

 deep mesial sinus that is about one-half the width of the shell at the front 

 margin ; sides sloping gradually away from the edges of the sinus and more 

 abruptly from the somewhat elevated upper portion. Dorsal valve much 

 more convex than the ventral and marked by a slight, broad mesial fold on 

 the lower portion;* beak strongly incurved; general surface rounding to the 

 margins from the central portions of the valve. 



Surface of the valves marked by from 40 to 50 round, simple plications. 



This species is distinguished from any described by its general form 

 and the numerous radiating plications. 



Formation and localities. Lower portion of the Carboniferous Group, 

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

 Canon, and on the northeast side of the canon north of Pinto Peak, Eureka 

 District, Nevada. 



Rhynchonella Thera, n. sp. 

 Plate vti, figs. 6, 6o-c. 



Shell small, subglobose or suboval, strongly convex, with a prominent 

 mesial elevation and suture. 



Ventral valve a little less convex than the dorsal, the greatest con- 

 vexity being on the posterior half; below the middle a broad, not very 

 sharply defined sinus begins, which becomes deeper and expands towards 

 the front; beak imperforate and slightly curved over that of the opposite 

 valve. 



Dorsal valve most convex at the middle; the median fold is not usu- 

 ally strongly defined ; it has a slight central sinus that reaches from near 

 the beak out to the front termination of the fold, the latter starting about 

 the center of the shell. Surface marked by fine concentric lines of growth. 



