Thus we have—
| Oriental Region | 1. Indo-Malay Sub-Region | (a) Indian Province |
| (b) Siamese Province | ||
| (c) Malay Province | ||
| (d) Philippine Province | ||
| 2. Chinese Sub-Region | (a) Chinese Province | |
| (b) Japanese Province |
The Indo-Malay fauna spreads eastward from its metropolis, but has practically no westward extension, or only such as may be traced on the eastern coasts of Africa and the off-lying islands. There appears to exist no other case in the world where the metropolis of a fauna is so plainly indicated, or where it lies, not near the centre, but at one of the ends of the whole area of distribution.
Comparing the two sub-regions, the Chinese is distinguished by the great predominance of Helix, while in the Indo-Malay sub-region Nanina and the related genera are in the ascendancy. In India itself there are only 6 genera of true Helicidae, poorly represented in point of numbers; in China there are at least three times this amount, most of them abundant in species. The Indo-Malay sub-region, on the other hand, is the metropolis of the Naninidae, which abound both in genera and species. In the Chinese sub-region Clausilia attains a development almost rivalling that of S.E. Europe, while in India there are scarcely a dozen species. A marked feature of the Indo-Malay sub-region is the singular group of tubed land operculates (Opisthoporus, Pterocyclus, etc.). In China the group is only represented by stragglers of Indian derivation, while the land operculate fauna, as a whole, is distinctly inferior to the Indian. Another characteristic group of the Indo-Malay region is Amphidromus, with its gaudily painted and often sinistral shell; the genus is entirely absent from China proper and Japan, where its place is taken by various small forms of the Buliminus group. Fresh-water Mollusca, especially the bivalves and operculates, are far more abundant in the Chinese sub-region than in the Indo-Malay.
(1) The Indo-Malay Sub-region.—(a) The Indian Province proper includes the peninsula of Hindostan, together with Assam and Upper and Lower Burmah. To the east and extreme north-east, the boundaries of the province are ill-defined, and the fauna gradually assimilates with the Siamese on the one hand and the Chinese on the other. Roughly speaking, the line of demarcation follows the mountain ranges which separate Burmese from Chinese territory, but the debatable ground is of wide extent, and Yunnan, the first Chinese province over the border, has many species common with Upper Burmah.
The gigantic ranges of mountains which bound the sub-region to the north-west and north limit the extension of the Indian fauna in those directions in a most decisive manner. There is no quarter of the world, even in W. America, where a mountain chain has equal effect in barring back a fauna. In the north of Kashmir, where the great forests end, there is a most complete change of environment as the traveller gains the summit of the watershed; but Kashmir itself distinctly belongs to the Indian and not the Palaearctic system. The great desert to the south of the Punjab is equally effective as a barrier towards the west.
The Mollusca of India proper include a very large number of interesting and remarkable genera. India is the metropolis of the great family of the Naninidae, or snails with a caudal mucus-pore, which are here represented by no less than 14 genera and over 200 species. The genera Macrochlamys, Sitala, Kaliella, Ariophanta, Girasia, Austenia, and Durgella are at their maximum. Helix is scarcely represented, containing only about 30 inconspicuous species (leaving Ceylon out of account). Buliminus is abundant, especially in the north. The Stenogyridae are represented by Glessula, which is exceedingly abundant in India, but has only a few straggling representatives in the rest of the Oriental region. Among the Pupidae is the remarkable form Boysia, with its twisted upturned mouth, while Lithotis is a peculiar form allied to Succinea, to which group also probably belongs Camptonyx, a limpet-like form with a very small spire, peculiar to the Kattiawar peninsula. Camptoceras, an extraordinarily elongated sinistral shell, with a loosely coiled spire, is peculiar to the N.W. Provinces.
Among the fresh-water pulmonates is an Ampullarina, a genus only known elsewhere from the Fiji Is. and E. Australia. Cremnoconchus is a form of Littorina, peculiar to the W. Ghâts, which has habituated itself to a terrestrial life on moist rocks many miles from the sea. The fresh-water operculates include the peculiar forms Mainwaringia, from the mouth of the Ganges (intermediate between Melania and Paludomus), Stomatodon, Larina, Fossarulus, Tricula, and others. The bivalves are neither numerous nor remarkable; Velorita, a genus of the Cyrenidae, is peculiar.
Fig. 202.—Characteristic Indian Mollusca: A, Hypselostoma tubiferum Blanf.; B, Camptoceras terebra Bens.; C, Camptonyx Theobaldi Bens.