12 BIOLOGICAL SOCIETY OF WASHINGTON. 



nental 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 tvvo principal areas are quite widely 

 separated, being in fact geographically almost wholly disassociated, 

 they possess a wonderful degree of similarity. Of the fifty com- 

 monly recognized families of mammalia occurring within its limits, 

 three-fifths are distributed 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 In- 

 dian Region ; all extend beyond it to the north\tard, five of them 

 even occurring over the greater part of the northern hemisphere. 

 Thus the African region is the more specialized division, only a 

 small portion of the tropical element in the Indian Region, through 

 which it is differentiated from the great Europeeo-Asiatic Temper- 

 ate Region, being unrepresented in the African, while the African 

 has three times as many peculiar families as the Indian." 



I am quite unable to appreciate the force of this exposition as an 

 argument in favor of the union of the two regions ; it appears to me 

 that it is, indeed, one that tells for the contrary side. Let it be re- 

 called that the ten families* peculiar to the African region are very 

 distinct, and that almost all of the eighteen families "common to 

 both regions " can be added to the twelve " of wide extralimital 

 range," if we take into consideration their distribution in even newer 

 Tertiary or sometimes Quaternary times. Further, the genera even 

 were, for the most part, of wide distribution formerly, and there is 

 strong reason to believe that the thirty forms '"'common to both 

 regions" were invaders of Africa in the later Tertiary, and that 

 among those now "peculiar to the African region " we have the 

 remnants of older faunae. If we revert to the fishes we find some 

 striking facts. These can be resolved under two categories. On 

 the one hand a number of forms are peculiar to Africa, or shared 

 in common with South America ; on the other are certain genera 



* There are really more. 



