VARIOUS SPECIES OF CTENODUS. 59 



and is longer than usual. Another orbicular species, about the 

 same size, has the margin less sinuous, and the hinge-line shorter 

 and not so well marked by lateral processes. Besides the above, 

 one or two much smaller but rather obscure kinds have occurred, 

 as well as separate plates of C. elegans. And one belonging to C. 

 ohliquus has been found connected with the palatal teeth and 

 scales. This and the scales will presently be described, along 

 with the oral armature of that species. 



Now, should it be denied that these large opercular plates be- 

 long to the C'tenodi, it may be asked to what other fishes of the 

 Coal-Measures can they be assigned ? PJdzoclus, Rhombo2)ty- 

 chius, and Megalichthys are the only large species that occur to 

 which they could, with our present knowledge, belong. The 

 other large Coal-Measure fishes are all Placoids, and are there- 

 fore out of the question. Rhizodus and lUiomhoptycldus are, 

 however, apparently closely allied to HolojJtychius, in which the 

 operculum is composed of more than one piece ; and in the for- 

 mer,' therefore, the gill-cover is in all probability similarly com- 

 posed ; while in Megalichthys the character of the enamel and 

 form of the operculum sufiiciently prove that the large opercula 

 above alluded to cannot belong to it. 



In the same shales likewise occur strong well-arched ribs, the 

 largest measuring six or eight inches in length. These also pro- 

 bably belong to the larger Ctenodi ; and this probability becomes 

 almost confirmed when we refer to the fact of the ossification of 

 the ribs in C. elegans, and that the proportion they bear in this 

 species to the length of the fish is just about the same that those 

 large ribs bear to the larger Ctenodi, which have been already 

 estimated at four or five feet long. These ribs cannot have 

 belonged to any of the other large species of our Coal system, 

 as none of them have, as far as known, ossified ribs ; neither 

 can they be assigned to Campylopleuron, a new genus recently 

 proposed by Professor Huxley''' for some large Coal-Measm-e 

 fishes found in Ireland, Avhich have not only ossified ribs, but 

 have also large opercula. These opercula, hoM'Cvcr, being 



♦•'Gcoluj^icnl Magn/.ino." Vol. HI.. \<.\W. 



