Collections of Mr. C. M. Woodford during his Second Expedition to the Archipelago." P. Z. S.. 1888, p. 470, pls. xx.-xxii.

(12) THOMAS, O.-" Catalogue of the Marsupialia and Monotremata in the Collection of the British Museum." London (1888).

(13)

"Description of a New Genus of Muridae allied to

Hydromys." P. Z. S., 1889, p. 247, pl. xxix.

(14) WALLACE, A. R.—“Island Life." London (1880).

(15) WIGLESWORTH. L. W.-" Aves Polynesia: a Catalogue of the Birds of the Polynesian Sub-region (not including the Sandwich Islands)." Abth. K. Zool. Mus., Dresden, No. 6 (1891).

(16) WILSON, S. B., and EVANS, A. H.-"Aves Hawaiienses: The Birds of the Sandwich Islands." Parts I.-IV., 4to. London (1890-93).

CHAPTER III

THE NEOTROPICAL REGION

(PLATE III., p. 82)

SECTION I-BOUNDARIES OF THE NEOTROPICAL REGION

THE Neotropical Region is, no doubt, after the Australian, the most distinct of all the regions. It includes not only the continent of South America, but the West Indies, Central America, and a considerable portion of Southern Mexico. As regards its northern termination, on account of the great admixture of Nearctic and Neotropical forms which takes place where the two Regions join, it is impossible to lay down anything but an approximate boundary. Mr. Wallace (11) draws the line from the mouth of the Rio Grande on the Atlantic side to the neighbourhood of Mazatlan, in about the same latitude, on the Pacific side, but bends it down between these two points so as to include in the Nearctic Region the whole of the high tableland down to the city of Mexico.

Some American naturalists, among others Merriam and Allen (1), include in the Neotropical Region the southern extremities of the peninsulas of Lower California and of Florida. This, however, appears to be unnecessary, at least so far as the mammals are concerned, though there are certainly a considerable number of Neotropical birds and insects found in both these districts.

Besides the mainland of Central and South America

and the West Indies, the Falkland Islands and the Galapagos must likewise be included in the Neotropical Region.

The West Indies form an important sub-region, containing some forms of great interest, and will be treated of in detail below.

The Falkland Islands are situated in the south Atlantic, about 250 miles east of the nearest point of Patagonia. They are, however, known to be connected with the mainland by a shallow sea of less than 100 feet in depth, and therefore present all the characteristic features of a "continental" group of islands. The only indigenous mammals are a Wild Dog (Canis antarcticus) and a Vesper-mouse (Hesperomys), which seem to be distinct, though closely allied to the mainland forms. The birds also are mostly identical with those of the mainland, though there are some just recognisable representative forms.

The Galapagos, a group of five larger and ten smaller islands, are situated in the Pacific, exactly under the Equator, at a distance of from 500 to 600 miles west of Ecuador. They rise up from very deep water, and are entirely of volcanic origin. They are therefore typical "Oceanic" islands. With the exception of two Vespermice, slightly differing from those of the mainland, and a peculiar Bat (Atalapha brachyotis), there are no indigenous mammals (2) in the Galapagos. There are, however, a considerable number of birds in these islands, most of them not found elsewhere, and many of them restricted to individual islands in which they represent each other (7).

There can be no doubt that the Galapagos have never,

at any period of their history, been joined to the mainland, and that, owing to the fact that they are situated in the region of equatorial calms, immigration from the mainland is very occasional. In this way has been gradually evolved the peculiar fauna, which, although highly specialised, shows abundant evidence of its having been derived from the nearest mainland.

SECTION II.-GENERAL VIEW OF THE MAMMAL-FAUNA OF THE NEOTROPICAL REGION

The Neotropical Region is essentially one of luxuriant tropical vegetation, the great mass of the land from Central America to Uruguay being occupied by vast forests. South of the tropic of Capricorn the woods soon disappear, and the country, over a large part of its surface, becomes a flat treeless expanse covered with more or less abundant pasture known as the Pampas, while all along the western coast extends the giant range of the Andes, the eastern flanks of which are, as a rule, well watered and wooded, while the western slopes from the Gulf of Guyaquil to the island of Chiloe facing the Pacific are utterly dry and arid. There are, however, also in the higher parts of Venezuela, the Guianas, and Brazil, open grassy plains called "campos," which rise as islands from a surrounding sea of evergreen tropical forest.

The mammalian fauna of the Neotropical Region is naturally a rich one, but in the number of genera and species falls considerably short of that of the Ethiopian Region. This may perhaps be accounted for by the physical features of the country, which are certainly not

so favourable for mammalian development as the more open and varied country of Africa.

This deficiency in mammalian life is, however, more than counterbalanced by the abundance of other groups of animals, more especially of birds and insects, to the development of which the luxuriant tropical vegetation seems to be especially conducive.

Again, the mammalian fauna of the Neotropical Region is quite as remarkable for what it does not possess (lipotypes) as for what it has. Everything points to the conclusion that during a long geological age, probably throughout the greater part of the Tertiary epoch, South America was entirely isolated from the rest of the world. Thus the present fauna has arisen from two quite different sources -first, from the original fauna of early Tertiary times; and, secondly, from immigrants from the north, some of these being of rather long standing, and others of later arrival.

Of the nine Orders of Terrestrial Mammals, representatives of eight occur in the Neotropical Region, the only Order entirely absent being the Monotremes, which are absolutely confined to Australia.

The Marsupials are represented in the Neotropical Region by a single family only, out of seven into which this order is usually divided. This is the Didelphyidæ, or Opossums, of the twenty-four generally recognised species of which one (Didelphys marsupialis) ranges north with some modification into the Nearctic Region. The Quica Opossum (D. opossum) (Fig. 7, p. 56) is another well-known

1 Since this was written Mr. Thomas has described his wonderful new South-American genus Canolestes, which seems to belong to the Australian Diprotodonts. See P. Z. S., 1895, p. 870.