FOSSILS OF THE LOWER SILURIAN. OU 
The surface presents a smooth, glistening appearance, and is marked 
by fine concentric stri and very fine, often scarcely perceptible radiating 
strie. This surface gives to fragments of the shell the character of some 
of the Linguloid shells. 
The species belongs, by its general form, to the group of which 7. 
(Ctenodonta) varicosa Salter (Mem. Geol. Surv. Gt. Brit., vol. iii, p. 345) and 
T. (C_) astarteformis Salter (Can. Org. Remains, dec. 1, p. 39, pl. viii, fig. 7) 
are the types; specifically it is distinct. 
Formation and locality—Upper part of Pogonip Group. Last slope of 
ridge east of the Hamburg Ridge, Eureka District, Nevada. 
Genus MODIOLOPSIS Hall. 
Modiolopsis occidens, n. sp. 
Plate i, fig. 5; pl. xi, figs. 14, 14a. 
Shell small, elongate, ovate in outline; broadest at the posterior half, 
contracting to about two-thirds the greatest width at the beaks; hinge-line 
nearly straight and a little more than half as long as the shell posterior to 
the beaks; posterior margin slightly convex and sloping obliquely from the 
extremity of the hinge-line to the rounded posterior end of the shell; the 
basal line curves downward, and then with a slight sinuosity, opposite the 
beak, extends nearly straight to the somewhat narrow, sharply rounded, 
anterior end; beak small, scarcely extending above the hinge-line, and sit- 
uated within the anterior third of the shell. The surface is moderately 
convex, most prominent along the posterior umbonal ridge, which is rather 
broadly rounded; umbonal slope abrupt and slightly convex. A broad, 
obscure mesial depression is shown on the lower part of the anterior half of 
the shell that does not extend up to the beak. 
Anterior muscular scar of medium size and well defined; posterior 
scar, pallial line, and exterior surface markings unknown. 
This species is related to Modiolopsis mytiloides Hall (Pal. N. Y., vol. 
i, p. 157, pl. xxxv, figs. 4a, 6) in its general outline, but differs in its less 
elongate form and in its position of its beaks. 
Formation and localities.—Pogonip Group, upper portion, Fish Creek 
