364 The American Geologist. June, 1895 
of numerous specimens of these fossils in the Cleveland shale 
of northern Ohio enables us to rearrange what we did know, 
and to add some new details which confirm and modify pre- 
vious opinion on the subject. To point out a few of these is 
the purpose of the present note. 
1. Spines. — When Prof. Traquair wrote his article for the 
Geological Magazine in 1888, the evidence for the presence or 
absence of spines on the cladodonts was insufficient for de- 
cision. So doubtful did this feature then appear to him that 
he even ventured to suggest the identity of Clenacanthus 
with Cladodus. "The thought has struck me" he says, "is it 
possible that this undoubted Cladodus may represent the den- 
tition of Ctenacanthus costellatus, the unique specimen of 
which, with the spines in situ, occurred in the same beds? It 
will be recollected that the only tooth visible in the specimen of 
Ct. costellatus was an imperfect one, but its median cusp was 
smooth. If there is any connection here the specimen of Ct. 
costellatus must have been a young individual, as these teeth 
indicate a fish of much smaller size." "This brings up once 
more the question of the correlation of Cladodus- and Ctena- 
canthus, a question which, I must admit, is still involved in 
great obscurity. When I wrote my description of Ctenacan- 
thus costellatus I was inclined to believe that Ctenacanthus 
and Cladodus represented the spines and teeth of the same 
genus, and that the genus itself was hybodont." 
Again Prof. Traquair writes regarding Chlamydoselachus : 
"I cannot, without farther evidence, accept Mr. Garman's ver}' 
confident assertion that Chlamydoselachus is a cladodont, 
leading, as it does, to the inference that Cladodus had no dor- 
sal spines." Again: "No spine is seen in the East Kilbride 
specimen, but as the body is absent, spines may have been 
borne by the fish when complete." 
Summing up, the professor writes: '■'Ctenacanthus hijhodoi- 
des has nothing to do with Cladodus, and as regards the other 
species I rather think that if we knew the creatures to which 
they belonged they would turn out to represent several types, 
possibly very dift'erent from each other." 
We have in these passages the record of the various changes 
of opinion which the gradually increasing light led professor 
Traquair to adopt regarding this group of fossil fishes, and it 
