FOSSILS OF THE LOWER SILURIAN. 83 
The cast of the outer whorl is round-oval in outline, the shell being 
thick and forming the carina seen on the outer surface. The presence of 
the basal carina distinguishes this species from any described form. 
Formation and locality—Upper beds of the Pogonip Group at Lone 
Mountain, 18 miles northwest of Eureka, Nevada. 
Interior casts of a species allied to this, and it may be the same, occur on 
White Mountain and the lower eastern slope of the ridge east of the Ham- 
burg mine, and at the same horizon on the Fish Creek mountains, Kureka 
District, Nevada. 
Maclurea, sp. ? 
Associated with the preceding at Lone Mountain there is a cast of a 
much larger and unusually flattened or compressed species. Owing to a 
doubt of this being its natural form, it was omitted in selecting specimens 
for illustration. In general form it is not unlike M. acuminata Billings 
(Pal. Foss., vol. i, p. 241, fig. 225, 1865), except that it is very shallow, not 
one-half the depth of the latter. 
Genus METOPTOMA Phillips. 
Metoptoma Phillipsi, n. sp. 
Plate i, figs. 4, 4a. 
General form of shell depressed conical; outline of base broadly 
elliptical to ovate; apex elevated and situated a little behind the anterior 
margin; sides gently convex or sloping, almost straight from the apex to 
the lateral margins; anterior slope from the apex to the margin slightly con- 
cave; posterior slope, from the apex to the posterior margin, broadly convex. 
Surface marked by fine concentric strize of growth, with a few stronger 
strie, or lines, at irregular intervals. 
Dimensions: greater diameter of base of large specimen, 23™™; lesser 
diameter, 17™™; height of apex above base, 10™. A small specimen gives 
8™" and 6™™ for the two diameters of the base, and 8™ as the height, show- 
ing that the relative proportions remain nearly the same in the young shells. 
I know of no closely related American or European species. Mr. Bil- 
lings has described a number of species from the Quebec and Trenton 
