ALLEN ON GEOGRAPHICAL DISTRIBUTION OF MAMMALS. 353 



of his " Lemuriaii Subregion ". Its northern boundary will be pro- 

 visionally considered as the northern mean annual of 70 F. 



As thus limited, the greater part of the Arabian Peninsula and the south- 

 ern portion of the Great Sahara belong to it. But just how much of the 

 latter belongs here, and how much to the Mediterranean Eegion, cannot 

 at present be readily determined. As already noticed, it consists largely 

 of transitional ground, and is as yet quite imperfectly known. It is to 

 some extent, doubtless, also a barrier region; but that it is by no means 

 an impassable obstacle is sufficiently shown by the large number of 

 generic types of mammals that extend from the Indian Kegion as far south- 

 ward even as the Cape of Good Hope. Even if it were an insurmount- 

 able barrier, the comparatively humid and fertile eastern coast border 

 would afford a sufficient highway of intercommunication between Trop- 

 ical Asia and Tropical Africa, and the community of life of the two 

 regions shows that for long ages there has been this open way of inter- 

 change. 



The African Eegion, considering its great extent and its tropical 

 climate, is to a great degree zoologically a unit, yet it is by no means 

 homogeneous. At least, three subdivisions may be recognized, each of 

 which is characterized by many peculiar genera. These subregious 

 have already been characterized by Mr. Wallace under the names of 

 Eastern, Western, and Southern. The Western (West African Province) 

 consists of the humid, heavily wooded region of the west coast, extend- 

 ing to a considerable, but at present not definitely determinate, dis- 

 tance into the interior, but probably with boundaries nearly as drawn 

 by Mr. Wallace.* The Eastern (East African Province) includes the 

 remainder of Intertropical Africa, while to the Southern (South African 

 Province) belongs the southern extratropical portion of the continent. 



Of these divisions, the Eastern contains the greatest number of genera, 

 as it likewise contains by far the greatest area; but it is the least spe- 

 cialized, only tiro -fifteenths of its genera being peculiar to it, while of the 

 genera of each of the other regions about one-fourth are peculiar. Nearly 

 one-half (about forty-four per cent.) of the genera of the Eastern Prov- 

 ince have a more or less general distribution over the whole African 

 Kegion, while only a little more than a third (thirty-three to thirty-eight 

 per cent.) of the genera of the other province have a similarly wide range. 



A much larger proportion of Indian genera are represented in the 

 Eastern and Southern Provinces than in the Western. This difference 

 Is due to obvious conditions, the fertile belt of the Nile district and ad- 

 joining coast forming an easy way of intercommunication between the 



* The conclusions and details here presented were worked out independently and de 

 novo by the present writer. That they agree so closely with the views and results 

 attained by Mr. Wallace, so far as Africa south of the Great Desert is concerned, is to 

 me a source of gratification. In order to avoid unconscious bias I purposely avoided 

 a detailed study of Mr. Wallace's writings on this subject till my own results were 

 written out, and on then comparing my own conclusions with those reached by Mr. 

 Wallace, became for the first time aware of their close agreement. 



