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Show 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. Gazella subgutturosa in characters, which I have above specified, stands exactly intermediate between the African and Central Asiatic Gazelles, and not only is it intermediate in the geographical distribution, but also in the physical character of its habitat. The second instance is that afforded by the small Gazelles from the Bogos country above mentioned, which are as intermediate in external appearance as they are in habitat between Gazella dorcas of Egypt and Gazella isabella of Senaar and Kordofan. The isolated position of Gazella euchore finds a parallel in the isolated character of reduced dentition. The most important deductions which appear to m y 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 Presidential Address to the Geological Society in 1870,1 shall conclude, merely stating m y conviction that in it lies the germ of the true explanation of the present distribution and differentiation of the entire group Antilope. " In fact the Miocene mammalian fauna of Europe and the Himalayan regions contains, associated together, the types which are at present separately located in the South-African and Indian subpro-vinces of Arctogaea. 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 and Upper Eocene epochs. Hence it becomes highly probable that the well-known similarities, and no less remarkable differences, between the present faunae 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 |