ORDER RHYNCHOCEPHALTA. 



II3I 



while Professor Seeley describes a centrale (navicular) in the tarsus. 

 The pectoral limb is considerably shorter than the pelvic (left side 

 of fig. 1035); and while both have five digits, neither presents any 

 very strongly marked divergence from the Rhynchocephalian plan 

 of structure. In the type species there were the normal two sacral 

 vertebrae ; but according to Professor Seeley, P. Linki differs from 

 all other known members of this branch in having three sacrals. 

 It is highly probable that Proterosaurus should be regarded as a 



Fig. 1035. — Part of the trunk and pectoral limb of Protei-osattrus 

 Speneri ; from the Permian of Thuringia. Reduced. (After von 

 Meyer.) 



specialised Rhynchocephalian. The imperfectly- 

 known genus Haptodus, from the Permian of 

 France, may not improbably indicate a Reptile 

 more or less nearly allied to Proterosaurus, 

 although on the other hand its affinities may be 

 with the Rhynchocephalian Palceohatteria. 



Order VI. Rhynchocephalia. — This order 

 is represented at the present day solely by the 

 remarkable genus Sphenodon {Hatterid), and may 

 be provisionally characterised as follows : The 

 external appearance is usually more or less lizard-like. In the skull 

 the quadrate is immovably fixed by its proximal extremity, and 

 unites by suture with the pterygoid ; an inferior temporal arcade 

 is present (fig. 1039); the postorbital, at least in Sphenodon, is 

 quite distinct from the postfrontal ; the palate is closed anteriorly 

 by the median union of the pterygoids, which, in the living form 

 at least, extend forwards to meet the vomers, and thus separate the 



