172 PALEONTOLOGY OF THE EUREKA DISTRICT. 
Genus NUCULA Lamarck. 
Nucula Rescuensis, n. sp. 
Plate xv, fig. 9. 
Shell small, broadly subovate, moderately convex; height to length 
as four to five; beaks not very prominent, about one-fifth the length from 
the broadly rounded anterior end; basal line broadly and uniformly curved; 
posterior end more sharply curved, and with the upper slope meeting the 
nearly straight hinge-line at an obtuse angle; posterior umbonal slope 
prominent and subangular. 
Surface, in the cast, shows evidence of concentric lines of growth 
where the cast is very perfect, otherwise it is smooth. 
Formation and locality—Middle to Upper Devonian horizon; Rescue 
Hill, west of Rescue Canon, Eureka District, Nevada. 
Nucula, sp.? 
Among the collections from Rescue Hill a number of casts of a larger 
species of Nucula than N. Rescuensis occur. Their form is much like that 
of N. Niotica of the Upper Helderberg Group of New York, but without 
some knowledge of the outer shell it is scarcely possible to determine 
whether it is that species, or a new form allied to some of the Devonian or 
Chemung species of New York. 
Genus DYSTACTELLA Hall. 
Dystactella insularis, n. sp. 
Plate xv, fig. 8. 
Shell transversely elongate-ovate, the length and height as two to 
one; valves moderately convex; anterior end contracted and sharply 
rounded at the extremity; basal line gently arcuate; posterior end some- 
what broadly rounded, the extremity coming above a line drawn through 
the transverse center of the shell; cardinal line a little curved; beaks 
depressed. 
Surface of cast marked by a strong anterior muscular scar; posterior 
scar not observed. 
