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period. At the beginning of Pliocene time, during the deposition of the Araucanian formation in Argentina and the Equus-beds” in the United States, a wide bridge between North and South America, affording an easy road to migrating animals, must have existed, and this again seems to have become considerably narrowed to form the present Isthmus of Panama.

LIST OF THE PRINCIPAL AUTHORITIES REFERRED TO

IN CHAPTER III.

(1) ALLEN, J. A.-“The Geographical Distribution of North American Mammals." Bull. Amer. Mus. N.H., iv., p. 199, 1892.

(2) ALLEN, J. A.—“On a Small Collection of Mammals from the Galapagos Islands, collected by Dr. G. Baur.” Bull. Amer. Mus. N.H., iv., p. 47, 1892.

(3) ALSTON, E. R.-"Biologia Centrali-Americana, Mammalia. London, 1879-82.

(4) CHAPMAN, F. M.—“Notes on Birds and Mammals observed near Trinidad, Cuba, with remarks on the Origin of West Indian Bird-life.” Bull. Amer. Mus. N.H., iv., p. 279, 1892.

(5) COPE, E. D.—“Description of two large extinct Rodents from Anguilla, West Indies, with remains of human art associated.” Proc Amer. Philos. Soc. Philad., xi., 1871, p. 183.

(6) LEIDY, J.-—“Remarks on Mylodon." Proc. Acad. Nat. Sci.' Philad., 1885, p. 49.

(7) SALVIN, 0.—“On the Avifauna of the Galapagos Archipelago.' Trans. Zool. Soc., ix., p. 447 (1876).

(8) SCLATER, P. L.-“Address to Section D. (Biology)." “Report of Forty-fifth Meeting of the British Association, at Bristol," p. 85 (1876).

(9) Thomas, 0.—“On Some Mammals from Central Peru.” P. 2. S., 1893, p. 333.

(10) TROUESSART, E. L.—“Note sur le rat musqué (Mus pilorides) des Antilles." Ann. Sci. Nat. Zool. (6), xix., No. 5 (1885).

(11) WALLACE, A. R.-—“The Geographical Distribution of Animals.” 2 vols. London, 1876.

(12) ZITTEL, K. A. von.—“The Geological Development, Descent, and Distribution of the Mammalia.” S. B. k. bayer. Akad. Wiss., xxiii., p. 137, 1893. Translation in Geol. Mag. (3), x., p. 401 (1893).

CHAPTER IV
THE ETHIOPIAN REGION

(PLATE IV., p. 122) SECTION I.-BOUNDARIES OF THE ETHIOPIAN REGION

The Ethiopian Region (see Map, Plate IV.) contains the whole of Africa south of the Sahara, together with Southern Arabia and the island of Madagascar. As in all other cases where there is a long land-frontier between two neighbouring Regions, so here it is impossible to lay down anything but an approximate line of demarcation between the Ethiopian and Palæarctic Regions.

The boundary usually adopted is the line of the Tropic of Cancer, which strikes Africa between Morocco and Senegambia, runs through the middle of the Sahara, crosses the Nile between the first and second cataracts, and passes through Arabia to the neighbourhood of Oman, on the Persian Gulf. Most of the country through which this line passes is desert, and its mammalian fauna is consequently meagre. Mr. O. Thomas (6) has recently published an account of a collection of mammals received at the British Museum from Oman, which shows, as would naturally be expected, that “the geographical relationships of this district are about equal with Africa and India; three of the species being distinctly African in affinities, three Indian, and the remainder either peculiar or widely spread and of no special significance.” On the whole,

therefore, the line of the tropic of Cancer, adopted by Wallace, seems to be a fairly suitable boundary.

Besides the island of Madagascar and its appendages, which contain one of the richest and most interesting of all known Insular Faunas, and form a very important Sub-region, which will be considered in greater detail below, the Ethiopian Region possesses other islands. These, however, are mostly Oceanic, and not of any great importance.

The Azores, Madeira, Canaries, and Cape Verde groups, although geographically African, seem to have derived their animals chiefly from Europe. They therefore belong to the Palæarctic Region, and will be dealt with under that head.

The islands of St. Helena and Ascension, situated in the South Atlantic, are both of them of volcanic origin, and separated from the mainland of Africa by more than 800 miles of deep water. Neither of these islands possesses any Vertebrates. The only land-groups well represented in them are the Beetles and the Land-shells—a study of which shows that the affinities of these islands are to Southern Europe and Southern Africa, but that the Fauna is in all probability an exceedingly ancient one; since its peculiarities are very great, and opportunities of migration of new forms to these islands have been few and far between.

The other islands in the Atlantic connected with Africa are Fernando Po, Prince's Island, St. Thomas, and Anno Bon, all situated in the Gulf of Guinea at various distances from its head. Fernando Po, an island of some 40 miles in length, but separated from the mainland by a somewhat shallow sea about 20 miles across is said to be

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