SQUAMATA. 195 



form its odontoid process ; there are also a basal piece, a large hypapo- 

 physis, and two lateral pieces. The axis bears a high neural spine. 

 The other cervicals bear separate hypapophyses. The chevron bones 

 are loosely articulated with the caudal centra. 



The genus Edestosaurus (Clidastes), typically represented in 

 the Upper Cretaceous of North America, comprises excessively 

 elongated animals, with vertebrae very commonly united by a 

 zygosphene-zygantrum articulation. One skeleton ascribed to 

 it exhibits much lengthened neural spines on some of the 

 vertebra? in the hinder half of the tail, suggesting the original 

 presence of a laterally compressed caudal fin. 



Sub-Order 3. Lacertilia. 



Palaeontology as yet affords no information concerning the 

 evolution even of the more specialized groups of lizards. All 

 the known fossils are very fragmentary. It is interesting to 

 note that during the early Tertiary period certain forms (e.g., 

 Iguana) now confined to the New World, were represented in 

 Europe a distribution paralleled by that of the fishes, Amia 

 and Lepidosteus, already mentioned (pp. 109, 113). It may 

 be also added that the most gigantic lizard hitherto discovered, 

 is an extinct Varanoid, Megalania prisca, known by numerous 

 vertebrae and a fragment of skull from the Pleistocene river- 

 deposits of Queensland. This is estimated to have been nearly 

 ten metres in length. 



Sub- Order 4. Ophidia. 



Except one fine specimen from the supposed Cretaceous of 

 Patagonia, the snakes are likewise known only by a few 

 imperfect Tertiary fossils, which scarcely admit of satisfactory 

 discussion. The detached vertebrae of Cretaceous age some- 

 times referred to this sub-order, are probably Dolichosaurian. 

 Typically ophidian vertebrae from the Lower Eocene of Sheppey 

 and the Middle Eocene of Bracklesham, are named Palcvophis 

 and ascribed to sea-snakes which may have attained a length of 

 six metres. 



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