MUSEUM OF COMPARATIVE ZOOLOGY. 27 
It will be remembered that, from my first mention of the genus, I have 
insisted on its resemblance to the Cladodonti. A further study of both 
extinct and recent forms enables me to speak still more positively in 
asserting that Chlamydoselachus 7s a Cladodont. As shown in the 
descriptions above, some of its teeth are so characterized as to make it 
imperative, if these teeth alone were considered, that the species should 
be placed in the genus Cladodus of Agassiz, and nearer than almost any 
of the fossil forms to his type C. mirabilis. It is only the fact that 
others of the teeth differ in base or cusps, or both, from those of any 
_ of the discovered species of that genus, that prevents the new shark 
from being placed in Cladodus. 
What were the shapes of the Cladodonts? is a question that has been 
asked a great many times by palzeontologists, but so far it has not re- 
ceived a satisfactory answer. Opinions generally have inclined toward 
the conclusion that the teeth of Cladodus belonged with the spines of 
Ctenacanthus. If we could say positively that the teeth of the former 
really belong with the spines of the latter, it would be a long step toward 
restoring the shape of the animal that bore them. The conclusion has 
been advocated by Thomson, Romanowsky, Hancock and Atthey, Barkas, 
and more recently by Dr. Traquair. Romanowsky has gone so far as to 
describe a species of Cladodus (C. tenwistriatus) from a spine alone. He 
does not state that he found spine and teeth associated directly, but 
that the discovery of the spine was made in a locality in which teeth of 
Cladodus mirabilis were numerous. According to Dr. Traquair, Barkas 
proposed to unite Cladodus, Hybodus, and Ctenacanthus. In the publi- 
cation cited, no reasons are given for the changes. Up to the time of Dr. 
Traquair’s publication, (Geol. Mag., Jan., 1884,) the relations of these 
genera have been merely matter of personal opinion, conjecture, sug- 
gested, as the Doctor puts it, by the obvious general resemblance of 
teeth of Cladodus and spines of Ctenacanthus to teeth and spines known 
to belong together in Hybodus. Others have held it probable that 
Psammodus or Orodus would prove the dentition of Ctenacanthus. Of 
all the contributions toward answering the question as to the dentition 
of Ctenacanthus, that of Dr. Traquair is the most important. In it he 
describes a new species, C’. costellatus, from a nearly entire fossil bearing 
the spines of that genus and teeth which certainly much resemble those 
of some Cladodonts. Only one of the teeth is sufficiently visible to give 
an idea of its shape, and this is a most unsatisfactory one. It hasa 
smooth, pointed, conical cusp on a broadish base which “looks as if it 
might support lateral denticles.” The lateral and posterior portions of 
