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, Eureka 

 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 Phillips!, n. sp. 

 Plate i, figs. 4, 4 a. 



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 striae of growth, with a few stronger 

 striae, or lines, at irregular intervals. 



Dimensions: greater diameter of base of large specimen, 23 mm ; lesser 

 diameter, 17 mm ; height of apex above base, 10 mm . A small specimen gives 

 8 mm and 6 mm for the two diameters of the base, and 3 mm 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 



