692 



PROP. T. H. HUXLEY OBSERVATIONS 



edentulous premaxillary and mandibular rostra, probably covered 

 with horn, the former received between the latter ; sometimes more 

 than one series of palatal teeth ; and either amphiccelous, or more or 

 less opisthocoelous, presacral vertebrae. 



This family contains Hyperodapedon and Rhynchosaurus, readily 

 distinguished by the cranial, vertebral, and dental differences given 

 above. 



The Sphenodonticlce have divided external nares ; a toothed pre- 

 maxillary rostrum, not horn-covered, nor received between mandi- 

 bular rostral processes ; a single series of palatal teeth ; and amphi- 

 coelous vertebrae. 



It is very interesting to observe that, so early as the Triassic epoch, 

 the group of the Sphenodontina had attained its highest known 

 degree of specialization, Hyperodapedon being in all respects a more 

 modified form than Sphenodon. It appears a probable conclusion 

 that in the Permian epoch or earlier, Lacertilia existed which were 

 less different from Sphenodon than either Byperodapedon or Rhyn- 

 chosaurus. 



I am unable to discover any feature in the organization of either 

 Hyperodapedon or Rhynchosaurus which supports the supposition, 

 sometimes entertained, that these reptiles departed from the types of 

 structure found among existing Lacertilia in any greater degree than 

 these (e. g. Monitor, Chamceleo, Gecko, Sphenodon) do from one another, 

 or that they present any approximation to other Orders of Eeptilia. 



The evidence now offered concurs with that afforded by the 

 structure of Telerpeton, in establishing the belief that the Lacertilian 

 type of organization had, in the Triassic epoch, attained perfectly 

 clear definition from all others ; and it further shows that, in 

 Hyperodapedon, the type had attained a degree of specialization on 

 a level with that exhibited by any modern Lizard. 



The relations of the Sphenodontina with other groups of Reptiles 

 of approximately the same age, in which the anterior ends of the 

 jaws tend to assume the characters of a beak, with or without 

 palatal teeth (Dicynodon, Endothiodon), and with such forms as 

 Placodus, cannot, I think, be profitably dealt with until more is 

 known of the organization of the latter. I may add that I am 

 unable at present to see any good grounds for the approximation of 

 Simcedoscmrus to Hyperodapedon. 



In his valuable account of the Indian species of Hyperodapedon 

 (' Indian Pretertiary Vertebrata,' vol. i. 1885), Mr. Lydekker assigns 

 various detached bones to this genus on very fair grounds of proba- 

 bility. The absence of intervertebral ossifications in H. Gorcloni, 

 however, would seem to diminish that probability so far as the 

 vertebrae are concerned. 



EXPLANATION OF THE PLATES. 



Plate XXVI. — Hyperodapedon Gordoni. 



Fig. 1, 2. Upper and lateral views of the skull. J nat. size. 



3. The palatal surface of the skull, so far as the adherent mandible 

 permits it to be seen, j nat. size. 



