FOSSILS OF THE DEVONIAN. 189 
from the apex to the acute periphery; transverse section subtrigonal; upper 
surface with a slight depression below the center; under surface slightly 
convex. Umbilicus closed. Aperture nearly round, with the inner lip 
reflected. 
Surface transversely marked by lines of growth that have a retral 
curve on the central portion of the upper surface of the volution. 
This species is doubtfully referred to Platyschisma, owing to its having 
a reflected inner lip and closed umbilicus. The latter, however, was prob- 
ably open in the earlier stages of growth, having been closed by the outer 
volutions. The general aspect of the species is much like that of several 
forms of Pleurotomaria occuring in the Silurian formations, but the 
absence of a definite mesial band and the presence of the broad sinuosity 
in the upper portion of the aperture, shown by the.retral curve of the 
lines of growth, distinguishes it and places its generic relations with Platy- 
schisma or an allied genus. 
Formation and locality —Upper horizon of the Devonian limestone, The 
Gate, Eureka District, Nevada. 
Genus CALLONEMA Hall. 
Callonema occidentalis, n. ‘sp. 
Plate xvi, figs. 3, 3a. 
Shell subglobose, depressed. Spire slightly elevated, consisting of 
about four rounded volutions very regularly increasing in size from the 
apex to the aperture; suture slightly depressed and marking the periphery 
of the preceding volutions. 
Surface exfoliated. The cast shows a few obscure transverse striz that 
curve gently backward from the suture towards the periphery. 
The general aspect of this species is similar to that of Callonema imitator 
H. and W. (Hall, Pal. N. Y., vol. v, pt. 2, p. 53, pl. xiv, figs. 16, 17) of the 
Upper Helderberg Group of the State of Indiana. It differs in having a 
more depressed spire, and the volutions expanding a little more rapidly. 
Formation and locality—lLower horizon of the Devonian limestone, 
Comb’s Peak, Eureka District, Nevada. 
