ALLEN ON GEOGRAPHICAL DISTRIBUTION OF MAMMALS. 351 



Genera of the South American Temxierate Realm. 



V. — THE INDO-AFRICAN REALM. 



The Indo-African Realm consists mainly of Intertropical Africa and 

 Intertropical Asia, to which it seems proper to add Extratropical South 

 Africa. The small portion of Africa south of the Southern Tropic lies 

 wholly within the warm-temperate zone. Its small extent and broad 

 connection with Tropical Africa render its separation as a distinct realm 

 (as I at one time rather hastily considered it) almost inadmissible, since 

 it is especially open to the influence of the great intertropical African 

 fauna, as is shown by the extension of many tropical forms down to 

 within a few degrees of its southern extremity. The area really pos- 

 sessing a temperate climate is restricted to its extreme southern border, 

 where alone appear the few generic and family types that do not have 

 a very general range over the tropical portions of the continent. This 

 area is many times smaller than the temperate portion of South 

 America, but, though so small, has quite a number of peculiar genera, 

 which impart to it quite distinctive features. It yet seems better to 

 regard it as an appendage of the great Indo-African Eealm rather than 

 as a distinct primary region. Madagascar, with the Mascarene Islands, 

 on the other hand, while perhaps possessing a closer affinity with Africa 

 than with any other continental region, has yet a fauna made up so 

 largely of peculiar types that it seems more in accordance with the facts 

 of distribution to regard it as a separate primary region. 



The Indo-African Realm, as thus restricted, forms a highly natural 

 division. Although its two principal areas are quite widely separated, 

 being in fact geographically almost wholly disassociated, they possess 

 a wonderful degree of similarity. Of the fifty commonly recognized 

 families of mammalia occurring within its limits, three-fifths are dis- 

 tributed throughout almost its whole extent. Of the remainder, one- 

 half are confined to Africa, and one is African and American, leaving 

 only nine in India that are unrepresented in Africa; three only of these 

 latter are, however, peculiar to the Indian Region 5 all extend beyond 

 it to the northward, five of them even occurring over the greater part of 



