and th&ir Relationship to Ceratodus Forsteri. 191 



elongated and scattered, or striated and punctate. The scales 

 alone would therefore seem sufficient for generic distinction. 



There are other characters, however, which distinguish the 

 two forms. When our paper on the subject was written, we 

 had not access to Pander's valuable ' Monograph on the Cte- 

 ?iddij)terini^*. Since then we have enjoyed this advantage, 

 and are now in a position to point out other features tliat 

 separate Dqjterus from Ctenodus. In the former the upper 

 dental plates are each adherent to the anterior extremities of 

 the two bones named by Pander res])cctively the palatal and 

 inner ])terygoid. These are elongated flattened bones, and lie 

 parallel to and in close contact with each other, being appa- 

 rently united by a suture. These conjoined bones form on 

 either side of the oral roof a flattened widish plate, with the 

 posterior extremity somewhat expanded. The two plates arc 

 united in front along the longitudinal middle line, and diverge 

 widely backwards. 



Now the upper dental plates of Ctenodus are usually found 

 attached to similar }:flate-like bones, which incline or diverge 

 to the right or left accordingly as they are united to the right 

 or left dental plate. These bony supports (PI. XIV. c, d) 

 are expanded at the posterior extremity, and are in general 

 configuration exactly like the plate composed of the palatal 

 and pterygoid bones in Dvpterus. Indeed there can be no 

 doubt that they are homologous ; but the fact to which we 

 wish to draw attention is, that while in Ctenodus the compo- 

 nent bones are united so as to form but one bone, the suture 

 being entirely obliterated, they are distinctly separated in 

 Dlpterus by a well-marked sutural line. This difference 

 would seem to be of some importance; for it appears to be 

 constant, as it occurs in all our species, of the whole of which, 

 excepting C. corrugatus^ these bones have been found. 



The sphenoid bones in the two genera are likewise very 

 different in character. In Dii^terus^ according to the same 

 high authority already quoted, as well as according to Hugh 

 Miller t, this bone is widely lozenge- formed, and does not 

 extend backwards very much beyond the extremities of the 

 palato-pterygoid bones to which the dental plates are attached, 

 and fills up the entire space between them : this bone Pander 

 considers the basi-sphenoid. 



In Ctenodus the sphenoid is a much elongated depressed 

 bone, with a wide lozenge-formed expansion near the anterior 

 extremity. In other words, the posterior angle of the lozenge- 



* * Ueber die Ctenodipterinen des Dovonischen Systems,' Dr. C. 11. 

 Pander. 1858. 



t See ' Footprints of the Creator,' p. 58. 



