CHELONIA. 175 



Sub-Order 2. Pleurodira. 



Although the living Chelonians of the sub-order Pleurodira 

 are almost exclusively confined to the southern hemisphere, 

 there is no doubt that many fragmentary fossils discovered in 

 the Upper Mesozoic and Lower Tertiary strata, both of Europe 

 and North America represent either typical members or ances- 

 tral forms of this group. The cervical vertebrae always exhibit 

 transverse processes, and the only means of retraction of the 

 head is by bending the neck on one side to rest within the 

 margin of the shell. The pelvis is articulated or firmly 

 anchylosed both with the carapace and plastron, the extinct 

 European and American genera, however, add nothing of impor- 

 tance to our knowledge of the morphology of these Chelonians, 

 and are of little phylogenetic interest. The remarkable genus 

 Miolania from Pleistocene deposits in Queensland, and from 

 Lord Howe's Island (nearly 400 miles distant from the 

 Australian coast), need alone be mentioned. The typical species, 

 M. oweni, from Queensland, must have attained a very large 

 size, the head measuring 0'58 m. in width to the tip of the 

 "horns." Both the head and tail (fig. 110) are armoured with 



Fio. 110. 



Miolania oweni; right lateral aspect of the extremity of the caudal sheath (A) 

 and anterior aspect of the cranium (B), about one-tenth nat. size Pleisto- 

 cene; Queensland. (After Owen.) 



large bony bosses symmetrically arranged, imparting to the skull 

 a horned appearance, and causing the tail to be enveloped in a 

 continuous bony sheath. Its carapace and plastron are almost 

 unknown. 



