THE GEOGRAPHICAL DISTRIBUTION OF MAMMALS 191 



which has two species, with two enlarged lower front teeth, 

 the sole survivors of a group which is abundantly represented 

 in the Tertiary deposits of Patagonia. 



The fauna of the Central American subregion is less rich 

 and characteristic than that of the Brazilian and is, to a cer- 

 tain extent, transitional to that of the Sonoran region of North 

 America, several genera proper to the latter region extending 

 into it, which are not known to pass the Isthmus of Panama, 

 such as shrews, a fox and one of the pocket-mice. The West 

 Indian islands are exceedingly poor in mammals, a great con- 

 trast to the East Indian, or Malay, Archipelago ; only a few 

 rodents, insectivores and bats occur in them. 



