(3) =Central-Asiatic Sub-region.=--The countries included in this vast sub-region are Turkestan, Songaria, Afghanistan, including the Pamirs, Western Thibet, and probably Mongolia. Kashmir belongs to the Indian fauna. At present the whole district is very imperfectly known; indeed, it is only at a few points that anything like a thorough investigation of the fauna has been made. It is therefore almost premature to pronounce any decided opinion upon the Mollusca, but all the evidence at present to hand tends to show that they belong to the Palaearctic and not to the Oriental system. This is especially the case with regard to the fresh-water Mollusca, many of which are specifically identical with those occurring in our own islands. A slight admixture of such widely distributed types as _Corbicula_ and _Melania_ occurs, but it is not sufficient to disturb the general European facies of the whole. It is possible that eventually the whole district may be regarded as a sub-region combining certain characteristics of the eastern portions of the Mediterranean basin with an extension of the septentrional element, due to higher elevation and more rigorous climate. The principal features in the land Mollusca appear to be the occurrence of a number of _Buliminus_ of the _Napaeus_ group, a few _Parmacella_ (Afghanistan being the limit of the genus eastward), _Clausilia_, _Pupa_, _Limax_, and _Helix_, with several stray species of _Macrochlamys_. =B. The Oriental or Palaeotropical Region= This region includes all Asia to the south of the boundary of the Palaearctic region, that is to say, India, with Ceylon, Burmah, Siam, and the whole of the Malay Peninsula, China proper, with Hainan and Formosa, and Japan south of Yesso. It also includes the Andamans and Nicobars, and the whole of Malaysia, with the Philippines, as far eastward as, and including Celebes with the Xulla Is., and the string of islands south of the Banda Sea up to the Ké Is. The Moluccas, in their two groups, are intermediate between the Oriental and Australasian regions. In this vast extent of land two distinct centres of influence are prominent--the Indian and the Chinese. Each is of marked individuality, but they differ in this essential point, that while the Chinese element is decidedly restricted in area, being, in fact, more or less confined to China itself and the adjacent islands, the Indian element, on the other hand, extends far beyond continental Asia, and embraces all the Malay islands to their farthest eastward extent, until it becomes overpowered by the Papuan and Australian fauna. Upper Burmah, with Siam, forms a sort of meeting-point of the two elements, which here intermingle in such a way that no very definite line of demarcation can be drawn between them. Thus we have--