184 PALEONTOLOGY OF THE EUREKA DISTRICT. 
Platyceras undulatum, n. sp. 
Plate vi, figs. 2, 2a. 
Shell small, depressed; apex incurved; body whorl expanding quite 
rapidly on the outer half of the volution; dorsum subangular and with a 
shallow depression on each side; a second rounded carina appears on the 
left side. The body volution is marked by concentric undulations that are 
slightly sinuous; on the dorsal carina a node appears at the crossing of the 
undulations. Aperture subcircular; peristome sinuate; the undulations 
corresponding to the outline of its margin. 
Surface of shell unknown. 
There is but one specimen of this species in the collections, but it 
is so well distinguished by its general form and the presence of trans- 
verse undulations that there is little danger of confusing it with other spe- 
cies It is of the same type as Platyceras Newberryi Hall (Pal. N.Y., vol. 
iii, p. 333, pl. Ixiii, figs. 14 a-e) of the Lower Helderberg Group, and the 
undulations in the cast may owe their origin to the presence of rows of 
nodes or spines on the shell. 
Formation and locality—Lower Devonian, Brush Peak, Eureka Dis- 
trict, Nevada. 
Platyceras thetiforme, n. sp. 
Plate vi, figs. 4, 4a, b. 
Shell obliquely arcuate from the base with the apex incurved, the nu- 
cleus making about one volution; body whorl gradually increasing in size 
to the aperture; on the back it is strongly carinate; the left side is evenly 
rounded and the right a little flattened, producing a slight carina where 
uniting with the anterior surface. 
Form of aperture unknown. Surface markings not determined. The 
strong carina on the back distinguishes this species from P. Thetis Hall, 
and its gradually expanding body volution, so much like that of P. Thetis, 
from P. carinatum. 
Formation and locality — Lower Devonian of Brush Peak, Eureka Dis- 
trict, Nevada, in association with Platyceras Conradi, Platyostoma lineatum, etc. 
