406 MESSRS. HANCOCK AND ATTHEY 



inclining backwards and downwards. In front the symphysial 

 surface is straight, extending the whole depth of the ramus, and 

 is grooved transversely. The dental plate is about two-thirds 

 the entire length of the ramus, and is placed nearer the sym- 

 physis than the posterior extremity. The ramus is upwards of 

 three inches in length, and, including the thickness of the dental 

 plate, is an inch deep. 



Such is the description of the ramus of C. obliquus, which, 

 with very little modification, would do equally well for all the 

 other species, as they vary only in size and slightly in the pro- 

 portions of the parts. On comparing this description and the 

 figure of the ramus (PL XIII., fig. 2), as well as that of the en- 

 tire mandible of C. wibricatus (fig. 1), with the representation 

 of the mandible of the so-called Ceratodus Forsteri that accom- 

 panies the paper on the subject in the " Proceedings of the Zoo- 

 logical Society," previously quoted, it will at once be seen that 

 these parts in this curious fish and those in Ctenodus closely re- 

 semble each other. So similar, indeed, are they, particularly in 

 the dentition, that, were nothing more known of the two forms, 

 they would both assuredly be considered to belong to one and 

 the same genus. 



And this likeness would be still greater if tbe cartilage were 

 present that undoubtedly originally supplemented the ramus of 

 Ctenodus. At present the outer border of the dental plate is 

 unsupported, overhanging as it does the side of the ramus. This 

 channel or cavity (PI. XIII., fig. 2, d) beneath the dental plate 

 must have been occupied by cartilage, which, passing backward 

 to the glenoid notch, might, it can easily be seen, form here a 

 semicircular cavity similar to that shown in the figure of the 

 mandible of Ceratodus Forsteri. The ramus would thus assume 

 a somewhat rotund form, instead of being a flattened, or rather, 

 a semicylindrical plate, as it has all the appearance of having 

 been, encasing incompletely a cartilaginous core. 



But, notwithstanding the similarity of the so-called Ceratodus 

 Forsteri to the Ctenodipterini, we are quite inclined to believe 

 that it will be found to be generically distinct from all known 

 forms. 



