1873.] SIR V. BROOKE ON THE GENUS GAZELLA. 553 



the furthest outposts of the group towards a common centre, and, 

 further, that in many instances the forms intermediate in position will 

 be found also intermediate in specific character. It will be perhaps 

 sufficient to refer to two instances. Oazella subgutturosa in charac- 

 ters, which I have above specified, stands exactly intermediate between 

 the African and Central Asiatic Gazelles, and not only is it interme- 

 diate in the geographical distribution, but also in the physical cha- 

 racter of its habitat. The second instance is that afforded by the small 

 Gazelles from the Bogos country above mentioned, which are as in- 

 termediate in external appearance as they are in habitat between 

 Gazella dorcas of Egypt and Oazella Isabella of Senaar and Kordofan. 

 The isolated position of Gazella euchore finds a parallel in the iso- 

 lated character of reduced dentition. The most important deduc- 

 tions which appear to my mind to be naturally suggested by these 

 facts are as follows : — 



1 . The platform upon which the Tertiary Antelope fauna existed 

 lying immediately to the north of that supporting the present fauna 

 offers a probability that the genera of the existing fauna were derived 

 directly from the extinct genera so closely resembling them. 



2. Gazella brevicornis being less specialized than existing Gazelles, 

 it is possible that from this form the existing forms closely resembling 

 it may have been derived. 



3. From the fact of outlying forms being more or less plainly 

 traceable towards a common centre, probability is afforded that the 

 line connecting the different forms more or less closely represents the 

 path along which evolution has taken place. 



With the hypothesis put forward by Professor Huxley in his Pre- 

 sidential Address to the Geological Society in 18/0, 1 shall conclude, 

 merely stating my conviction that in it lies the germ of the true ex- 

 planation of the present distribution and differentiation of the entire 

 group Antilope. 



" In fact the Miocene mammalian fauna of Europe and the Hima- 

 layan regions contains, associated together, the types which are at 

 present separately located in the South-African and Indian subpro- 

 vinces of Arctogsea. Now there is every reason to believe, on other 

 grounds, that both Hindostan south of the Ganges and Africa south 

 of the Sahara were separated by a wide sea from Europe and North 

 Asia during the Middle aud Upper Eocene epochs. Hence it be- 

 comes highly probable that the well-known similarities, and no less 

 remarkable differences, between the present faunse of India and 

 South Africa have arisen in some such fashion as the following : — 

 Some time during the Miocene epoch, possibly when the Himalayan 

 chain was elevated, the bottom of the Nummulitic sea was upheaved 

 and converted into dry land, in the direction of a line extending 

 from Abyssinia to the mouth of the Ganges. By this means the 

 Dekhan on the one hand and South Africa on the other became 

 connected with the Miocene dry land and with one another. The 

 Miocene mammals spread gradually over this intermediate dry land. 



" The fact that this immense fauna of Miocene Arctogaea is now 

 fully and richly represented only in India and South Africa, while it 



