100 THE NEOG^IC REALM. [CHAP. 



carapace smooth ; each being perforated by three or four large 

 holes for the passage of blood-vessels, and the whole being pro- 

 bably invested with a continuous leathery skin, instead of each 

 disc bearing a separate horny shield. Commencing with a small 

 series of enormous, narrow, hoop-like rings, the tail-sheath termi- 

 nates in a long, massive, depressed, and nearly smooth club- 

 shaped tube, at the extremity of which are a number of rough 

 disc-like surfaces, apparently for the attachment of large horns. 



None of the preceding forms, which include all the largest 

 members of the family, range below the horizon of the Monte 

 Hermoso, Catamarca, and Parana beds, but the group is also 

 represented in the Santa Cruz deposits of Patagonia, although the 

 single species found there is of much smaller dimensions than any 

 of its later cousins, the whole length of the carapace not exceeding 

 about two feet. It is noteworthy that this earliest known glypto- 

 dont, on which the unwieldy name of Propalczohoplophorus has been 

 conferred, presents certain indications of affinity to the armadillos 

 in the structure of its carapace, in which incipient movable bands 

 may be detected on the margins of the middle region. In this 

 small size of their earliest definitely known representative, the 

 glyptodonts resemble the under-mentioned ground-sloths. 



Unless the aforesaid remains from the Oligocene Phosphorites 

 of France should prove to belong to the group, we are at present 

 totally in the dark as to whence both the glyptodonts and the 

 armadillos originally came ; and it is, indeed, quite probable 

 that, like the other members of the order, they may have origi- 

 nated in South America (if not in an Antarctic continent) from 

 some at present quite unknown mammalian type. How such 

 creatures, which seem absolutely unassailable, came to be extermi- 

 nated, is one of those questions which it appears quite impossible 

 to answer. 



Although they have not hitherto been discovered in a fossil 

 state, the sloths, constituting the family Bradypodidce, 

 are just as characteristic of Neogaea as the two pre- 

 ceding groups. Their habits, however, necessarily restricting them 

 to the tropical forest-districts, their absence in a fossil state 1 must 



1 A presumed fossil sloth was described from the Argentine, but the jaw on 

 which it was founded proves to belong to the Megalotheriidce. 



