TORTOISES AND TURTLES. 27 



mosaic-like plates of the carapace of the former 

 resemble the plates of the bony armour of the 

 crocodiles, and are probably derived from a 

 primitive armature of this kind. If this be so, 

 then the bony plates of other Chelonians must 

 be regarded as a later development, the origin of 

 which is yet to be discovered. This is the view 

 most generally favoured at the present time, and 

 accordingly, we must look upon the Leathery 

 Turtle as the sole survivor of a primitive and 

 independent group. 



Parallels are always interesting, and it is 

 seldom that they cannot be found in the animal 

 world, however remarkable the instance we may 

 have to match. 



Thus, though the shell of the Tortoise has no 

 counterpart among the living reptiles, we find a 

 very close resemblance thereto in the shell of cer- 

 tain gigantic and extinct mammals the S. Ameri- 

 can Armadillos, known as Glyptodonts. These 

 creatures were encased, like the Chelonia, in a 

 bony shell, which in some forms is as much as five 

 feet long, and an inch in thickness. The struc- 

 ture of this shell resembled that of the Leathery 

 Turtle, in that it was made up of a series of 

 small bones closely interlocked to form a mosaic, 

 but different therefrom in that each of these 

 bony plates was covered by a horny shield. As 

 in the Chelonia, the separate bones of the verte- 

 bral column were welded together to form a tube. 

 The limb-girdles, however, did not occupy the 

 anomalous position which they held in the 

 Chelonia, inasmuch as they bore the same rela- 

 tion to the skeleton as in other animals. 



