HISTORY OF THE EDENTATA 595 



deltoid and supinator ridges and epicondylar foramen; the 

 fore-arm bones are always separate, and there is generally much 

 freedom of rotation of the manus. In the wrist there is no 

 distinct central and usually there are the ordinary eight sepa- 

 rate bones. The tibia and fibula are frequently coossified. 

 The tree-sloths, which lead most strictly arboreal lives and are 

 almost helpless on the ground, are unique among mammals in 

 that the body is habitually suspended from the limbs, not carried 

 upon them ; the feet are curved hooks, which fit over the tree- 

 branches and support the weight without muscular exertion. 

 The limb-bones are very long and slender, the claws long, 

 curved and sharp, and the metapodials of each foot, two or three 

 in number, are fused into a single mass. In the fground-sloths 

 there was much change in foot-structure during the course of 

 their recorded development ; they were usually five-toed and 

 the feet were armed with one or more great claws ; the later 

 and larger representatives of the suborder walked upon the 

 outer edge of the feet. 



The armadillos, which are largely burrowers, have five- 

 toed feet and long, heavy, pointed claws, but in some of them 

 the pes has a varying number of flat, hoof-like nails. The 

 immense fglyptodonts had very short, broad feet, shod with 

 hoofs, which, in some of the genera, were longer and more 

 claw-like in the manus. 



The recorded history of the edentates was developed almost 

 entirely in South America. In the Casa Mayor formation there 

 were numerous armadillos, but as only scutes of the carapace 

 have been found, little is known of them. The fground-sloths 

 {\Protohradys) have been reported, but from such imperfect 

 material that the reference is uncertain. The first assuredly 

 determinable members of this suborder were in the Astra- 

 ponotus beds and, associated with them, the most ancient 

 known fglyptodonts. In the Deseado stage were many 

 armadillos, some of them extremely peculiar, several fglypto- 

 donts and fground-sloths, some species of the latter very 



