MANDIBULAE AND PALATAL TEETH OF CTEXODUS. Ill 



examined, or that tlie other teeth had a similar formation ; he 

 figures a section magnified a very few diameters, which only shows 

 the medullary canals branching and anastomosing in an homo- 

 geneous matrix, and such is the opinion the Professor held of the 

 minute anatomy, for he distinctly states that there are not any 

 calciferous tubules nor eanaliculi {sic) permeating the osseous 

 part of the tooth. Undoubtedly he was right in pourtraying what 

 lie saw, but we will see shortly that even with . a low power 

 dentinal tubules can be easily perceived, and that when they are 

 absent it is because of the thinness of the section. 



Professor Owen, in his " Odontography," remarks that the 

 texture presents a coarse osseous base supporting a dense osseous 

 or enamel-like layer, which statement is very indifferent and 

 might be applied to a great number of the teeth of Cestraciont 

 genera and species. Many years after the appearance of this 

 work. Professor Owen published a booklet entitled " On the 

 Dental Characters of Carboniferous Eishes and Batrachia," but 

 which was immediately withdrawn from circulation, as it was at 

 once seen that every tooth he described and had raised into a new 

 genus or species had been known, named, and described years 

 previously. Among these so-called new genera was Sagenodits, 

 the species inequalis, the description of which was accompanied by 

 beautifulty coloured lithographs, but neither the letter-press nor 

 the figures differed in one essential point from the account of 

 Ctenodits structure as published by Messrs. Hancock and Atthey 

 in the " Annals of Natural History" and the " Transactions of the 

 Northumberland and Durham Natural History Society." 



A somewhat brief description of the minute structure of these 

 teeth was given by Messrs. Hancock and Atthey in a paper entitled 

 " Notes on the E/Cmains of some Eeptiles and Fishes from the 

 Shales of the Northumberland Coal Field," which appeared in the 

 3rd volume of the above " Transactions" ; they took C. cristatus 

 for their purpose ; they, however, did not figure the structure. 



Mr. T. P. Barkas does not refer to the microscopical characters 

 in any of his writings on this subject, but he gives coloured litho- 

 graphs of them in the "Atlas" accompanying his " Coal Measure 

 Palaeontology." 



This is all the literature bearing upon this portion of my paper, 

 and it will be seen that it is too meagre for purposes of com- 

 parison ; the figures, however, of Agassiz and Barkas are excellent 

 considering the low powers they employed. As I have said, the 

 structure of the teeth of Ctenodi is similar in detail whatever 

 species may be taken, but undoubtedly they can be made to 

 differ markedly to all appearance by cutting sections in different 

 situations and directions, but when a section of a tooth of one 

 species is compared with an exactly similar cutting of the tooth 

 of another these differences disappear. 



