FISHES OF THE CARBONIFEROUS SYSTEM. 181 
similarity to the under surface of the brain of certain animals. It is evident 
from these characters that they did not rest on any hard, smooth substance, 
like the jaw which supports the flattened teeth of Psammodus, etc., and we 
must conclude that they were set upon or implanted in comparatively soft 
tissue. 
Formation and locality: Base of Cuyahoga shale; immediately over 
Berea grit, Berea, Ohio. Collected by Dr. William Clark and Prof. William 
Kepler. 
CTENACANTHUS ANGUSTUS, N. Sp. 
Spine ten inches long by one inch wide at broadest part, gently and 
uniformly arched; laterally compressed ; exposed portion occupied by rela- 
tively few and broad closely pectinated ridges, of which the strongest, of 
double average width, forms the anterior margin; this is annulated by 
closely set transverse lines, while on the lateral ridges the cross lines are 
slightly oblique, rising backward; the ridges are about twelve in number on 
each side at the middle of the spine. 
This species, by its more slender form and few strong enamel ridges, 
may be distinguished at a glance from Ct. Clarkit, N , with which it is asso- 
ciated, and these features serve also to separate it from most others known. 
In general form it is not unlike Ct. formosus,’ N., but it is somewhat more 
robust and has not half the number of longitudinal ridges. From C7. furct- 
carinatus, N. (loc. cit.) it is also separated by the latter character, though the 
pectination of the ridges is similar. 
Formation and locality: Berea grit; Berea, Ohio. Collected by Dr. 
William Clark. 
Section E.—FIsHes oF THE CARBONIFEROUS LIMESTONE. 
The central member of the Carboniferous system—the Mountain Lime- 
stone of England, the Bergkalk of Germany, the Calcaire Carboniftre of 
France, the Sub-carboniferous or Lower Carboniferous limestone of Ameri- 
can geologists—has been described in general terms on the preceding pages. 
Since it is a marine deposit of great thickness, and therefore the evidence 
‘Paleontology of Ohio, vol. 2, p. 53. pl. 59, fig. 1. 
