UPON" HYPEKODAPEDON GOKDONI. 



689 



It is obvious, even from these imperfect data, that the hind foot 

 of Hyperodapedon was longer than the fore foot, though shorter in 

 proportion than that of Sphenodon. It seems also in the gradation 

 of the digits to have departed less from the ordinary Lacertilian foot 

 than the fore foot does. 



The comparison of all parts of the skeleton, which has now been 

 made, leaves no doubt as to the close relations between Hyperodapedon 

 and Sphenodo?i, At the same time it makes clear the existence of a 

 number of differences, of which the following appear to me to be the 

 most important : — 



1. The centra of the praesacral vertebrae are ossified throughout 

 and more or less opisthoccelous, especially in the cervical region. 

 Moreover there are no intercentral ossifications. 



2. The anterior cervical vertebrae have long and strong ribs. 



3. The external nares are not separated by bone. 



4. The conjoined premaxillary processes form a long, conical, 

 curved, pointed rostrum, which is received between two rostral pro- 

 cesses of the mandible. All these were devoid of teeth, and probably 

 en sheathed in horn. 



5. The palatal area is very narrow in front and wide behind, with 

 strongly curved lateral boundaries. 



6. The posterior maxillary and palatal teeth are multiserial. 



7. The rami of the mandible are united in a long symphysis, 

 behind which they diverge widely, and their dentigerous edges are 

 strongly concave upwards as well as outwards. 



8. The mandibular teeth are set into a close, apparently continuous 

 palisade in front, and they become distinct and conical only at the 

 posterior end of each series. 



9. The fore foot is remarkably short and stout, with metacarpals 

 of equal length. I find no evidence of the existence of an " ect-epi- 

 condylar foramen " in the humerus. 



IlJiync7iosaurus, although allied to Hyperodapedon, is sharply dis- 

 tinguished from the latter by its vertebral and cranial, characters ; 

 and, in some respects, it occupies an intermediate place between 

 Hyperodapedon and Splienodon. 



A specimen in the British Museum (to which I shall refer as No. 1) 

 shows the head and trunk in almost undisturbed relation, though much 

 damaged in some parts. The length, from the snout to the sacrum, 

 could not have exceeded 280 millim. ; so that the animal was only 

 a little larger than the specimen of Splienodon of which the measure- 

 ments are given above ; and, as the skull was about 80 millim. long, 

 it had about the same proportion to the trunk as in Sphenodon. 



The centra of the thoraco-lumbar vertebrae are about 10 millim. 

 long and amphicoelous. They present, at each end, a hemispherical 

 concavity, each of which occupies about a fourth of the length of the 

 centrum, the two middle fourths being occupied by bone. No 

 specimen which I have seen shows the characters of the centra of the 

 cervical or sacral vertebrae, nor throws any light upon the question 



