CHAPTER XI GEOGRAPHICAL DISTRIBUTION OF LAND MOLLUSCA (_continued_)--THE ETHIOPIAN, NEARCTIC, AND NEOTROPICAL REGIONS =D. The Ethiopian Region= The Ethiopian region includes the whole of Africa south of the Great Desert, and Southern Arabia, together with the outlying islands, excepting those of the Atlantidean province (p. 297). Regarded as a whole, the Ethiopian is poorest in land Mollusca of all the tropical regions. And yet its characteristics are very remarkable. The entire _Achatina_ group is peculiar, and takes, especially in W. Africa, some curious forms (_Columna_, _Perideris_, _Pseudachatina_). Carnivorous Mollusca (_Ennea_, _Gibbus_, etc.) are highly developed, especially in the south and east, the largest known helicoid form (_Aerope_) being from Natal. In the possession of these types of the Agnatha, Africa is more closely related to the Australasian than to the Oriental region. The true _Cyclostoma_ are entirely peculiar to the region, but are absent from West Africa. Fresh-water Mollusca are abundant and characteristic, especially in and near the Great Lakes. _Lanistes_, _Cleopatra_, and _Meladomus_, among the operculates, together with _Mutela_ and _Aetheria_ (Unionidae), _Galatea_ and _Fischeria_ (Cyrenidae), are peculiar. In its negative, as well as its positive features, the Ethiopian region is markedly isolated. Helicidae and Naninidae are equally deficient, the former, indeed, attaining some numerical predominance in the extreme south, but the species are nearly all insignificant in size and colouring. It is only in Madagascar that _Helix_ asserts itself. _Arion_, _Limax_, _Hyalinia_, _Clausilia_, and a number of other genera abundant along the Mediterranean, are either altogether absent, or are very scantily represented. Land operculates, so characteristic of other tropical countries, are almost entirely wanting. If we disregard the Malagasy sub-region, there are scarcely forty species of land operculates on the whole African continent. The Ethiopian region may be divided into three sub-regions: (1) the Central African; (2) the South African; (3) the Malagasy. (1) =The Central African Sub-region= is bounded on the north by the Great Desert, on the east and west by the ocean, and on the south by a line roughly drawn between the mouth of the Orange River and Delagoa Bay; it also includes S. Arabia. No natural features exist which tend to break up this vast district into areas of independent zoological development. The absence of long and lofty mountain ranges, the enormous size of the great river basins, and the general uniformity of climate, equalise the conditions of life throughout. It will be convenient to break the sub-region up into provinces, but in most cases no precise line of demarcation can be laid down.