and their Relationship to Ceratodus Forsteri. 197 



physis than the posterior extremity. The ramus is upwards 

 of three inches in length, and, inchiding 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 tlie 

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

 proportions of the parts. On comparing this description and 

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

 the entire mandible of C. imbricatus (fig. 1), with the repre- 

 sentation of the mandible of the so-called Ceratodus Forsteri 

 that accompanies the paper on the subject in the ' Proceedings 

 of the Zoological Society,' previously quoted, it will at once 

 be seen that these parts in this curious fish and those in Cte- 

 nodus closely resemble 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 con- 

 sidered to belong to one and the same genus. 



And this likeness would be still greater if the 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 ranms 

 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 cartilagi- 

 nous core. 



But, notwithstanding the similarity of the so-called Cera- 

 todus Forsteri to the Ctenodipterini^ we are quite inclined 

 to believe that it will be found to be generically distinct from 

 all known forms. 



The new Australian fish is described to have two " incisor " 

 teeth in the upper jaw, placed a little in advance of the dental 

 plates. There is no reason for believing that such additional 

 teeth are present in either Dipterus or Ctenodus. Several 

 entire heads of the former have been obtained ; and we possess 

 in the specimen before alkidcd to of C. elegans a crushed head 

 of that species, and have also two crushed heads of C. obliquus • 

 and in neither genus has there been found the least trace of 

 any such " incisor " teeth. The four dental plates only are 

 present — two palatal, two mandibular. And, again, these 

 plates are not by any means uncommon at Newsham, where 

 upwards of four hundred specimens have been obtained by 

 Mr. Atthey. Had such " incisors " existed, about two hun- 



