and their Relationship to Ceratodus Forsteri. 195 



been found, which are divisible into five or six species by the 

 modification in the form ; they are paired bones. Their ge- 

 neral character is that of a flattened elongated bone, with one 

 end a little expanded, arched slightly, and gradually thinned 

 out to a fine edge ; it narrows a little towards the other end : 

 one of the lateral margins is slightly thickened, and is some- 

 what convex ; the opposite margin is a little concave. From 

 the narrow extremity a strong wide process is given off at right 

 angles, and extends considerably beyond the concave margin. 



These bones vary a good deal in size and form : some are 

 comparatively narrow and much elongated ; others are short 

 and broad ; but all have the right-angular process at the 

 nan-ow extremity. The largest are 4f inches, and the smallest 

 f inch in length. 



These hatchet-shaped bones undoubtedly belong to Ctenodus, 

 as they frequently occur with the remains of that fish ; and a 

 right and a left specimen have been found in connexion with 

 a crushed head of C. obliquus, which fine cranial example exhi- 

 bits three of the dental plates, both opercula, the sphenoid, the 

 occipitals, and several other bones of the head. No jugular 

 plates have been found ; but as they are present in Dipterus, 

 they may be expected to occur in Ctenodus, 



The Hon. William Forster's most interesting discovery of 

 the extraordinary fish which Mr. Gerard Krefft has described 

 under the name of Ceratodus Forsteri^ will, no doubt, in due 

 course throw a flood of light on these curious Devonian and 

 Carboniferous genera, with which it evidently has much in 

 common. Its relationship to Ceratodus^ however, is perhaps 

 doubtful. From Mr. Krefft's description*, it appears that in 

 Ceratodus Forsteri the skeleton is only partially ossified, in 

 this respect agreeing with i)/pfer?<s and Ctenodus • but from 

 what is known of Ceratodus, the latter is probably a true 

 cartilaginous fish, and consequently a Selachian or Placoid. 

 If this were not the case, surely something more would be 

 known of it than the mere dental plates, which do not seem to 

 be uncommon, but which are never found, so far as we know, 

 in connexion with bony supports, with palatal or mandibular 

 bones. In Ctenodus, on the contrary, which has the palatal 

 bones and mandible ossified, the dental plates usually occur 

 attached to them. Mr. Atthey has in his collection numerous 

 specimens of the dental plates adhering to entire rami and 

 perfect palato-pterygoid bones. Specimens of all the species, 

 excepting C. corrugatus, occur in this state ; and, in fact, some 

 portion of the bony sujiport is almost always present. The 



• Proc. Zool. Soc. 1870, part 2, p. 221. 



14* 



