138 Geological Society. 



The recently discovered ffyperodaiyedon-skeleton was of nearly 

 the same size as that formerly described, and must have belonged 

 to an individual about 6 or 7 feet in length. The specimen was 

 exposed by the splitting of a large block of sandstone, and comprised 

 the skull, the vertebral column as far as the root of the tail, all the 

 bones of the left and of part of the right fore limb, and those of the 

 right hind limb, the whole almost in their original relations. 



The bones were described in order and compared with those of 

 Sphenodon, the most important dilSerences in Hyperodapedon being 

 the following : — 



1. The centra of the presacral vertebrae are ossified throughout 

 and more or less opisthocoelous, especially in the cervical 

 region. 



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



3. The external nares are not separated by bone. 



4. Conjoined premaxillary bones form a long, conical, curved, 

 pointed rostrum, which is received between the rostral pro- 

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

 probably sheathed in horn. 



6. 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 the dentigerous edges 

 are strongly concave upwards as well as outwards. 



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

 continuous palisade, and become distinct and conical only 

 at the posterior end of the series. 



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

 carpals of equal length. 



The relations of Rliynchosaurus to Hyperodapedon and Sphenodon 

 were then dealt with, the first-named being shown to occupy 

 in some respects an intermediate place between the two others. 

 The skull of Rhynchosaurus resembles that of Hyperodapedon in its 

 single anterior nasal aperture, its premaxillary and mandibular 

 rostral processes, and in having more than one series of palatal 

 teeth ; but in general form and in the shape of the maxillae, palatal 

 bones, and rami of the mandible it departs far less from Sphenodon 

 than Hyperodapedon does. Some comparisons of the limb-bones were 

 also made. 



The three genera mentioned were shown to form a particular 

 group, which, however, had no claim to ordinal distinction, and 

 appeared to form a family, Sphenodontidse, of the Lacertilia, com- 

 prising two subfamilies, Rhynchosaurinae (including Rhynchosaurv^ 

 and Hyperodapedon) and Sphenodontinae. 



The fact that in this Lacertilian group the highest known degree 

 of specialization, as shown in Hyperodapedon, was attained as early 

 as the Triassic epoch, showed that iu Permian times, or earlier, 

 Lacertilia existed which differed less from Sjphenodon than either of 



