28 BULLETIN OF THE 



the base are not seen, and there seem to be no rudimentary denticles. 

 What is exposed favors to some degree the conclusion of its discoverer ; 

 but we do not know that the tooth has the lateral cusps, the backward- 

 expanded base, or the rudimentary denticles of the typical species of 

 Cladodus. 



The probability is that Cladodus, known only from dentition, — which 

 would include teeth of Rhina or the upper front teeth of Heptabranchias, 



— contains species that, if living to-day, would be distributed among a 

 number of genera, or even among different families. This being the case, 

 it might not be out of the way for Dr. Traquair to claim that Ctenacan- 

 thus — with a short body, two dorsals each with a spine, a mouth simi- 

 lar to that of Heterodontus, and teeth with one cusp and no buttons — 

 is a Cladodont; while Chlamydoselachus — with elongate body, a spine- 

 less dorsal, an ophidian mouth, and teeth with lateral cusps and buttons 



— is claimed to represent Cladodus itself, 



Chlamydoselachus, however, has not been an undisputed Cladodont. 

 In several publications Professor Cope has asserted its identity with 

 Diplodus of Agassiz (renamed Didymodus by Cope, but later admitted to 

 be identical with Xcnacanthus). As he has since abandoned his posi- 

 tion, it would be unnecessaiy to consider the subject further, if it were 

 not that he has made no publication of his change of opinion, and that 

 matter in one or two of the communications may be used to throw 

 light on the affinities of Chlamydoselachus and allied sharks. From 

 the American Naturalist of April, 1884, page 412, we quote the fol- 

 lowing description of skulls said by its writer to belong to the genus 

 Diplodus Ag., renamed Didymodus, in which Mr. Cope claimed the 

 frilled shark must be placed (see page 22). 



*' The palatopterygoid arch is suspended to the postorbital process of the cra- 

 nium, as ill the existing Flexanchidae. The genus would then be referred to the 

 suborder Opistharthri of Gill, but for the following peculiarities : The skull is 

 segmented, so that cartilage-frontals, parietals, and occipitals can be distin- 

 guished, together with an element which has the position of the intercalare. 

 The occipital supports a large vertebral cotylus. There are membrane bones 

 extending from the nose over tlie orbits, which are either supraorbitals or 

 frontals. The tissue of the bones is granular, which leads to the belief that the 

 granular ossification which covers the chondrocranium in recent sharks, pene- 

 trated the entire chondrocranium in this genus. Hence the basicranial axis 

 consists of the sphenoid and presphenoid bones. One at least of the nares is 

 on the superior face of the muzzle. The frontal cartilage-bones are elevated 

 and fissured at the posterior extremity, each apex projecting freely upwards and 

 backwards, presenting a certain resemblance to the structure seen in the Lepi- 



