TOKTOISES AND TURTLES. in 



and the presence of an intergular shield in the plastron 

 (Fig. 30) is absolutely characteristic. The members 

 of this group are termed Pleurodirans, or side-necked 

 tortoises, and, as we have said, are now exclusively 

 confined to the Southern Hemisphere, and are the only 

 Chelonians met with in Australia. In former epochs 

 this group was, however, much more widely distributed, 

 so that we may probably conclude that the Pleuro- 

 dirans are an older and less specialised type than the 

 Cryptodirans. A very remarkable gigantic fossil tor- 

 toise from Queensland and Lord Howe Island, which 

 may probably be regarded as a member of the Pleuro- 

 diran section, is remarkable for having large horn-like 

 prominences on the skull, and also for the bony rings 

 with which the tail was protected, somewhat after the 

 fashion of the Glyptodont Mammals (see page 16). 

 Finally, the soft tortoises form a third group, allied 

 to the Cryptodirans in the mode of retraction of the 

 head, but distinguished by certain peculiarities in the 

 structure of the skull and shell. From the presence 

 of only three claws on the feet of the typical forms, 

 this group is technically termed the Trionychoidea ; 

 and with it we bring to a close our remarks on 

 tortoises. 



