FISHES OF THE CARBONIFEROUS SYSTEM. 171 
cone compressed, with sharp edges; both faces arched, though unequally ; 
anterior face marked by four to six strong longitudinal costz, reaching from 
the base to the upper third, which is smooth and highly polished ; lateral 
denticles, two on either side, exterior pair much the larger, coarsely 
costate. 
The remarkably coarse ridges of the anterior face of the central cone, 
together with the size of the teeth, will serve to distinguish this from any 
species before described. Some of the teeth of smaller species of Cladodus 
have a few coarse ridges on the posterior or anterior face or both, such as 
C. carinatus, described in this memoir; C. costatus, N. & W. ete.; but none 
of these are likely to be mistaken for the species under consideration. 
A large number of teeth of this species have been obtained by Mr. Park 
Terrell from the Cleveland shale in the valley of Black River, Lorain County, 
Ohio. About seventy-five of these were lying in contact or so closely 
approximated that they may be regarded as belonging to the dental series 
of one fish. These show great differences in size, some being an inch in 
height and breadth, while others are not more than one-quarter of that size. 
Between these extremes there is a gradation in size, but all are essentially 
alike in form and markings; having like characters and found in such rela- 
tions, it is certain that they belonged to one fish. . 
An interesting fact in connection with this set is that many of the teeth 
have the central cone truncated by wear. This means that the teeth of 
Cladodus were more permanent than those of most of our modern sharks. 
Apparently a large number were in service at the same time, and they 
remained for the most part in position and effective during the life of the 
individual. 
A jaw of a small species of Cladodus (C. Pattersoni) found at Vance- 
burgh, Ky., still carrying teeth, shows ten or more rows set alternately, and 
covering the arch of the jaw just as do the crushing teeth of Rhynchobatus. 
The figures now given represent three medium-sized teeth, one of which 
is slightly, another much worn, the third truncated by use. 
The species is dedicated to Mr. Park Terrell, principal of the Institution 
for the Dumb and Blind at St. Augustine, Fla. He was formerly the com- 
1 Geol. Survey Illinois, vol. 2, p. 27, pl. 1, fig. 13. 
