FOSSILS OF THE DEVONIAN. 



173 



In general appearance this shell resembles a Nuculites or Palseoneilo, 

 but it is without the clavicular ridge of the former and the faint muscular 

 scars of the latter. In the presence of the strong anterior muscular scar, 

 the somewhat nasute anterior end and the rounded up posterior extremity 

 it is allied to Dystactella subnasuta, Hall (Pal. N. Y., vol. v, pt. 1, Plates and 

 Explanations, p. 14, pi. li, figs. 28-3!, 18'83) from the Upper Helderberg 

 rocks of the Falls of the Ohio. 



Formation and locality. Lower part of the Devonian limestone in the 

 lower or central area of Gray's Canon, Eureka District, Nevada. 



Genus MEGAMBONIA HalL 



Megambonia occidualis, n. sp. 

 Plate v, fig. 1. 



Outline subcircular. Length and breadth subequal. General sur- 

 face strongly convex, with a convex anterior wing separated from the 

 body of the shell by a well-marked, slightly curved sinus. Hinge-line 

 shorter than the width of the shell. 



Right valve unknown. Left valve with the beak depressed and curv- 

 ing forward over the cardinal line. Area and interior characters unknown. 



Surface marked by strong concentric striae and lines of growth; a few 

 radiating lines are shown in the posterior half of the shell. 



The most nearly related species is Megambonia subcordjformis Hall 

 (Pal. N. Y., vol. v, pt. 1 ; Plates and Explanations, pi. Hi, figs. 1, 8). The dif- 

 ferences are the less elongate form and the character of the surface markings. 



Formation and locality. Lower Devonian; Lone Mountain, 18 miles 

 northwest of Eureka, Nevada. 



Genus NYASSA Hall. 



Nyassa parva, n. sp. 

 Plate xv, figs. 14, 14 a. 



Shell small, transversely elongate, with the cardinal and basal margins 

 subparallel, the posterior end being a little broader than the anterior; the 



