The Mollusca of Formosa, although in many cases specifically distinct, show close generic relationship with those of China. The characteristic Chinese groups of Helix and Clausilia occur, and there is still a considerable Indian element in several species of Streptaxis, Macrochlamys, Kaliella, and Alycaeus. The occurrence of two Amphidromus, a genus which, though Siamese, is not found in China or Hainan, is remarkable.
The peninsula of Corea must undoubtedly be included in the Chinese sub-region. It is true that the land operculates scarcely occur, but there are still a number of Clausilia, and several of the characteristic Chinese groups of Helix are reproduced. In some points Corea appears to show more affinity to Japan than to China, four of the Helices being specifically identical with those of Japan, but the peninsula is at present too little explored for any generalisations to be made as to its fauna in this respect.
(b) Japanese Province.—Kobelt distinguishes four groups of Mollusca inhabiting Japan (a) circumpolar species, actually occurring in Europe, Siberia, or N. America, or represented by nearly allied species (these of course do not belong to the Japanese province as such); (b) Indo-tropical species; (c) species which are Chinese or akin to Chinese; (d) peculiar species, a mixture of two forms, southern and northern, the latter being chiefly Hyalinia, Patula, and Fruticicola. Out of a total of 193 Japanese species, at least 164 are peculiar.
The Japanese Helices belong to sub-genera common to China (Plectotropis 8, Euhadra 21, Acusta 23?); but the Naninidae scarcely occur at all. The principal feature of the fauna is the development of Clausilia, which presents some extraordinarily fine forms. One slug (Philomycus) is identical with an Indian species. The operculates, which consist mainly of a few species each of Diplommatina, Cyclophorus, Pupinella, Pupina, Helicina, and Georissa, belong almost exclusively to the southern islands Kiu-siu, Sikoku, and southern Niphon. The three species usually reckoned as Japonia are probably forms of Lagochilus.
C. The Australasian Region
This region includes all the islands of the Pacific east of the Moluccas, and falls into three sub-regions—the Papuan, the Australian, and the Polynesian.
1. The Papuan Sub-region may be divided into—(a) the Papuan Province proper, which includes New Guinea, with the Aru Is. and Waigiou, the Admiralty Is., New Ireland, New Britain, and the d’Entrecasteaux and Louisiade Groups; (b) the Queensland Province, or the strip of N.E. Australia from C. York to the Clarence R. (about 29° S. lat.); (c) the Melanesian Province, which includes the New Hebrides, New Caledonia, with the Loyalty Is. and the Viti Is. The Solomons form a transition district between the Papuan and Melanesian provinces, abounding on the one hand in characteristic Papuan Helices, while on the other they form the north-western limit of Placostylus, the group especially characteristic of the Melanesian province.
(a) The Papuan Province.—The molluscan fauna of New Guinea is the richest and by far the most original of all the Australasian region. We find ourselves, almost in a moment, in a district full of new and peculiar forms. New Guinea may be regarded as the metropolis of the rich Helicidan fauna, which is also characteristic of the Moluccas to the west, of N. and N.E. Australia to the south and south-east, and of the Solomons and other groups to the north-east. Here abound species of Papuina and Insularia (the latter being quite peculiar), among which are found, if not the largest, certainly the most finished forms of all existing Helices. Chloritis (13 sp.), Planispira (5), and Cristigibba (9) are common with the Moluccas, while a tropical Australian element is shown in Pedinogyra (1) and Hadra (4). Very remarkable, too, is the occurrence of one species of Obbina and Rhysota, genera which culminate in the Philippines and here find their most eastward extension; while a single Corasia serves to form a link between the Corasia of the Philippines and those of the Solomon Is., if the latter are true Corasia.
We naturally find considerable traces of a Polynesian element, which appears to be principally characteristic of the eastern part of the island. Most noteworthy in this respect is the occurrence of Partula (3), Tornatellina (1), Charopa (1), Thalassia (3). As compared with the true Pulmonata, the operculates are feebly represented, and the great majority are of a markedly Polynesian type. Not a single Cyclophorus occurs; Lagochilus, Alycaeus, and all the tubed operculates, so marked a feature of the Indo-Malay fauna, are conspicuous by their absence, and the prevailing genera are Cyclotus, Helicina, and a number of sections of Pupina. Leptopoma, as in the Philippines, is strongly represented. Not that an Indo-Malay element is altogether absent. We still have Xesta (5), Hemiplecta (8), and even Sitala (2), but the great predominance of Helix seems to have barred the progress, for the greater part, of the Indian Naninidae.
The slugs appear to be represented by a solitary Vaginula. A single Perrieria is a very marked feature of union with Queensland, where the only other existing species (P. australis) occurs. The solitary Rhytida, so far the only representative of the carnivorous group of snails, emphasises this union still further. Little is known of the fresh-water fauna. Melania (28 sp.) is predominant, but on the whole the relations are Australian rather than Indo-Malay. Ampullaria is wanting, while a decisive point of similarity is the occurrence of Isidora (3 sp.), a genus entirely strange to the Oriental region, but markedly characteristic of the Australasian.