206 CRITIQUES AND ADDRESSES. [ix. 



teristically South -American Rodent, of a Sloth, an Arma- 

 dillo, or an Ant-eater has yet been found in Miocene 

 deposits of Arctogeea, I cannot doubt that they already 

 existed in the Miocene Austro-Columbian province. 



Nor is it less probable that the characteristic types of 

 Australian Mammalia were already developed in that 

 region in Miocene times. 



But Austro-Columbia presents difficulties from which 

 Australia is free ; Camelidce and Tapiridce are now 

 indigenous in South America as they are in Aretogsea ; 

 and, among the Pliocene Austro-Columbian mammals, 

 the Austro-Columbian genera Equus, Mastodon, and 

 Machairodus are numbered. Are these Postmiocene 

 immigrants, or Praemiocene natives ? 



Still more perplexing are the strange and interesting 

 forms Toxodon, Macrauchenia, Typotherium, and a 

 new Anoplotherioid mammal (Homalodotherium) which 

 Dr. Cunningham sent over to me some time ago from 

 Patagonia, t confess I am strongly inclined to surmise 

 that these last, at any rate, are remnants of the popula- 

 tion of Austro-Columbia before the Miocene epoch, and 

 were not derived from Arctogaaa by way of the north 

 and east. 



The fact that this immense fauna of Miocene Arctogaea 

 is now fully and richly represented only in India and in 

 South Africa, while it is shrunk and depauperized in 

 North Asia, Europe, and North America, becomes at once 

 intelligible, if we suppose that India and South Africa 

 had but a scanty mammalian population before the 

 Miocene immigration, while the conditions were highly 

 favourable to the new comers. It is to be supposed that 

 these new regions offered themselves to the Miocene 

 Ungulates, as South America and Australia offered them- 

 selves to the cattle, sheep, and horses of modern colonists. 

 But, after these great areas were thus peopled, came the 



