80 Mr. T. Attliey on various Species o/'Ctenodus 



single piece, are equally distinct ; tliey are thick and ■well- 

 rounded, being only slightly elongated transversely, and have 

 the upper or hinge-margin flattened, the surface irregularly 

 granulated, punctured, and enamelled. The tail is in a con- 

 fused state ; but there can be little doubt that it is heterocercal, 

 of the rhomboidal type. And there are traces of an anal and 

 a ventral fin immediately before the caudal ; but it is impos- 

 sible to say whether or not they are lobed. There are a few 

 slender, curved bones scattered about behind the head, which 

 have the appearance of ribs ; these and the bones of the head 

 alone have been ossified ; the vertebrae have all disappeared. 



Such is the description of C. elegans^ so far as it can be 

 determined by the imperfect remains of the specimen in my 

 possession. That it is specifically distinct from the Old-Red- 

 feandstone species is evident enough ; and it seems quite 

 probable that it even differs from them generically. It is 

 much smaller than most of the Dijyteri — though it is apparently 

 not full-grown, as the teeth are considerably smaller tlian the 

 largest specimens of them belonging to tliis species in my 

 possession ; and, on account of its minuteness when com- 

 pared with the largest species of Ctenodus from the coal- 

 measures, there is some doubt whether it may not be generi- 

 cally different also from them. It is not more than three 

 inches long, as has been already stated, while three at least of 

 the larger species cannot be less than four or five feet from 

 head to tail. The sphenoid bones previously mentioned of 

 C. eJegans are together about half an inch long ; the same 

 bones of the large species alluded to must have been at least 

 eleven inches in length. 



From the fragments of a large sphenoid and palatal bones 

 in my possession, it is possible to restore this portion of a 

 skull that probably belonged to G. cristatus^ which is not the 

 largest species ; and we are thus enabled to form an approxi- 

 mate estimate of the size of the head, which must have been 

 upwards of twelve inches long and nine broad. Therefore, 

 assuming the proportions to be similar to those of G. eleganSy 

 we arrive at the conclusion that these large Gtenodi were not 

 less than four or five feet in length. 



This estimate of the size of these animals receives some 

 support from the fact that very large opercular plates occur in 

 tlie same shales in which the palatal armature is found. I 

 have in my possession six or seven different kinds of opercula, 

 all having the essential characters of those found in connexion 

 with the head of G. eJegans ; that is, they agree with them in 

 the roundness of their form, in being composed of a single 

 solid piece, and in the smface-granulation and enamel. So 



