MUSEUM OF compaeatht: 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 is 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 palaeontologists, 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. tenuistriatus) 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 has a 

 smooth, pointed, conical cusp on a broadish base which " looks as if it 

 i7iight support lateral denticles." The lateral and posterior portions of 



