82 Mr. T. Attliey on various Species of Ctenodus 



ribs cannot have belonged to any of the other large species of 

 our coal-system, as none of them have, so far as known, ossi- 

 fied ribs ; neither can they be assigned to Campylophuron, a 

 new genus recently proposed by Prof. Huxley * for some large 

 coal-measure fishes found in Ireland, which have not only 

 ossified ribs, but have also large opercula. These opercula, 

 however, being " characterized by a raised longitudinal rib," 

 differ from those of Ctenodus, which have no such process or 

 " rib." 



All the tooth-plates described in the sequel of this commu- 

 nication have such a general resemblance to each other that 

 there can be no doubt of the close relationship of the fishes to 

 wliich they belong. And, moreover, the bones to which many 

 of them are found attached closely resemble each other. The 

 palatal tooth (or that which has been so designated) is seated 

 on a broadish flattened bone which, with one exception, is 

 never more than twice the length of the tooth, and is usually 

 considerably shorter ; and it is always much expanded at the 

 posterior extremity. This is probably a maxillary bone ; and 

 chc two branches, when united, have much the appearance of 

 vn upper jaw. The propriety, therefore, of calling these pa- 

 latal plates or teeth may be questioned. The homologies, 

 however, of these parts must be left for the present untouchedf. 

 The mandibular tooth is always much narrower than the pa- 

 latal, and the branch of the mandibulum on which it is placed 

 is not so wide as the bone supporting the palatal tooth, neither 

 is it so much expanded at the posterior end ; it is, however, 

 strong and rather massive. 



There are two species that have the surface of the teeth 

 with smooth ridges, not tuberculated or denticulated as they 

 are in all the other kinds. These two have consequently 

 some resemblance to the palatal plates of Ceratodus, apparently 

 a closely allied form. When further research shall have 

 thrown more light on these obscure species, it will then be 

 time enough to consider the desirableness of dividing this appa- 

 rently natural group into separate genera. 



I shall now conclude this brief communication with concise 

 descriptions of the various dental plates that have come under 

 my observation, retaining the denomination of palatal plates 

 or teeth for the upper pair, though the bones to which they 

 are attached have all the appearance of maxillaries, and so 

 they will be named in the following descriptions. 



* Geol. Mag. vol. iii. p. 166. 



t This matter is undoubtedly discussed in Prof. Pander's ^Monograph 

 on the Ctenododipterini ;' but I'have not seen that important Avork. 



