262 LAND MAMMALS IN THE WESTERN HEMISPHERE 



same three suborders are found in both formations. One of 

 the few tground-sloths that have been obtained was very 

 large {\Octodontherium crassidens), a much larger animal than 

 any species of the suborder that is known from the Santa Cruz. 

 The t&lyptodonts were also rare, and only two genera and 

 species have been described from very scanty remains. Arma- 

 dillos, on the other hand, were much more common, and no less 

 than eleven genera have been named, three of which occurred 

 also in the Santa Cruz. Among these was the remarkable 

 genus ]Peltephilus, in which the anterior two pairs of plates of 

 the head shield were modified into horn-like spines. 



Equally striking was the remarkable diminution of the 

 Rodentia, as compared with those of the Santa Cruz, though, 

 of course, this is an inaccurate mode of stating the truth, 

 occasioned by the fact that we are following the history in 

 reverse order. It would be preferable to say that the rodents 

 underwent a remarkable expansion in the Santa Cruz, These 

 rodents of the Deseado stage are the most ancient yet dis- 

 covered in South America and represent only two families, 

 both belonging to the Hystricomorpha, or porcupine group. 

 If, as Dr. Schlosser and other European palaeontologists main- 

 tain, the Hystricomorpha were all derived from a family of 

 the European Eocene, this would necessitate a land-connection 

 between South America and the Old World independent of 

 North America, for the latter continent had no hystricomorph 

 rodents until the connection between the two Americas was 

 established. 



The great bulk of the Deseado fauna is made up, so far as 

 individual abundance is concerned, of hoofed animals belong- 

 ing to the typically South American groups. The fToxodonta 

 were represented partly by genera which were the direct 

 ancestors of the common Santa Cruz genera {'fPronesodon, 

 '\Proadinotherium) , and, more numerously, by a very peculiar 

 family, the fNotohippidse, which had highly complex, cement- 

 covered grinding teeth. Still a third family of this suborder, 



