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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,1 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.
species of the group, which is found all through the Region, from Southern Mexico to La Plata.
The third Order of mammals-the Edentata-is highly characteristic of the Neotropical Region. Of the five
generally recognised families two belong entirely to the Old World; the other three-the Sloths, the Ant-eaters, and the Armadilloes (which are more nearly allied to one another than to the two Old World families)-are, with the exception of one species of Armadillo (Tatusia
novemcincta), which extends into Texas, absolutely confined to the Neotropical Region, and are eminently characteristic of its mammal-fauna. The Sloths (Bradypodide) of the present epoch at least, are entirely arboreal
in their habits, and pass their lives suspended by their limbs on the underside of the branches of trees (Fig. 8). The Ant-eaters (Myrmecophagidae) are also mainly inhabitants of forests, and one of the three existing forms (Cyclothurus) is exclusively arboreal. A second (Tamandua) may be said to be semi-arboreal, but the largest-the
Great Ant-eater as it is usually called (Fig. 9)-does not climb trees, though mostly found in forest-districts. These three animals are all widely distributed in the woodlands of tropical America, but never met with elsewhere. The Armadilloes (Dasypodide) are mostly inhabitants of more open districts (see Fig. 10, p. 59). Besides the three living
families of Edentates, there are two (the Megatheriida and Glyptodontidae) now extinct, which are chiefly characteristic of the Neotropical Region, though remains of them have also been found in certain formations in North America (6).
The fourth order of mammals, the Ungulates, is very poorly represented in the Neotropical Region, four only out of the fourteen usually recognised families being found within its limits. The Peccaries (Dicotylida) consist of only two species, of which one (D. tajacu) ranges as far
north as the Southern United States, and the other is confined to the Neotropical Region. A second family, the Camelida, is shared by the Neotropical Region with the Old World. The representatives of this family in the New World are the Lamas, belonging to the genus Lama (see