Ithynchucephalia. 29 



with five digits, liad a remarkable resemblance to the "flippers " Wall-case, 

 of a whale {see Fig. 33). ^°- 7- 



Fig. 36. — The imperfect skull of Mosasaurus Comperi (Meyer), from the 

 Upper Cretaceous of Maestrlcht, Holland (much reduced). 



Order V.— RHYNCHOCEPHALIA (Beak-headed Lizards). 



This order has only one living representative, the genus Wall-case, 

 Sphenodon {Hatteria), from 'New Zealand. Its earliest known ^°' ®' 

 ancestor, PalceohaUeria, dates from the Permian. In external 

 appearance the Rhynchocephalians were lizard-like animals. 

 They have the quadrate bone of the skull immovably fixed by 

 the proximal extremity to the pterygoid, the palate is closed 

 anteriorly by the median union of the pterygoids which ex- 

 tend to the vomers ; the premaxillao are never united. The 

 teeth are acrodont, being ancbylosed to the jaws. Abdominal 

 ribs are always present. 



Under the name of Hhynchosaurus articeps, Sir Richard Rhyncho- 

 Owen described and figured, in 1842, a very interesting reptile saurus. 

 from the fine-grained white Triassic sandstone of the Grinsill Wall-case, 

 quarries near Shrewsbury (Trans. Cambridge Phil. Soc, vol. 

 vii., part iii., p. 355, pi. 5 and 6). The vertebra are biconcave, 

 but whilst in some characters of the processes they resemble 

 recent lizards, in others they present characters like those of the 

 Dinosauria. The skull presents the form of a four-sided pyranrid 

 compressed laterally ; it is also remarkable for the beak-like 

 prolongation of the premaxillaries, which are pointed and re- 

 curved, and may have been encased in a horny sheath, like the 

 mandible of a bird of prey. It had also, like the still existing 

 New Zealand lizard Sphenodon (Hatteria), to which it is closely 

 allied, two rows of minute acrodont teeth, united to a sharp 

 edge of the maxillary and palatine bones respectively, between 

 which the teeth of the lower jaw fit in a longitudinal groove. 



