The Malay peninsula is practically another island of somewhat the same shape and general trend as Sumatra, and about one-half the size. Its general relations—and the remark applies to the great Sunda Islands as well—appear to be rather more with Burmah, Tenasserim, and even the Cingalese district, than with Siam. Points of connexion between Ceylon and Sumatra, and Ceylon and Borneo, have already (p. 304) been brought out.

It seems not impossible, from the point of view of the land Mollusca only, that the Sunda Islands may at one time have stretched much farther into the Bay of Bengal, prolonged, perhaps, into what are now the Andaman and Nicobar groups, while Ceylon and the western side of the Deccan, united into one continuous piece of land, and possibly separated from N. India by a wide stretch of sea, extended farther eastward in a long island, or series of islands.

Java, from its Mollusca, does not appear to hold the comparatively isolated position which its mammals and birds seem to indicate. Borneo, on the other hand, is more Siamese than Java or Sumatra in respect of a group whose metropolis is Siam, namely, the tubed operculates; for while that section is represented by 3 species in Sumatra and only 2 in Java, in Borneo it has as many as 19, Rhiostoma not occurring in the two former islands at all. Alycaeus, Lagochilus, Pupina, and Cyclophorus are found throughout, but Hybocystis (Malacca, 1 sp.) does not quit the mainland. Borneo is remarkably rich in land operculates, especially noticeable being the occurrence (11 sp.) of Opisthostoma (Fig. 208), a most extraordinary form of land shell (Ceylon, Siam), of Diplommatina (17 sp.), and Raphaulus. The occurrence of a single Papuina (Moluccas eastward) is very remarkable.

Amphidromus is a genus characteristic of the great Sunda Islands, attaining its maximum in Java (12 sp.). The Indian Glessula still has one species each in Sumatra, Java, and Borneo. One species of Streptaxis[369] occurs in Malacca, but Ennea (3 sp.) reaches as far east as Borneo and the Philippines. Parmarion, Helicarion, Ariophanta, and other groups of the Naninidae are well represented. Hemiplecta and Xesta are abundant and large, while the Rhysota of Borneo contain some huge sinistral forms. Rhodina is a remarkable form from Malacca, whose exact generic position is not yet settled. Clausilia has a few species on all the islands, the last occurring on Ternate, and a single Papuina (Moluccas and N. Guinea) occurs in Borneo.

The Island of Celebes marks the beginning of a distinct decrease in the Indo-Malay element. The Naninidae lose ground, in proportion to the Helicidae, Macrochlamys, for instance, being represented by only one species, and Hemiplecta by four. Other characteristic genera of the Indian region dwindle, such as Amphidromus, Clausilia, the tubed operculates, and Cyclophorus, while Sitala, Kaliella, Glessula, and Plectotropis disappear altogether. Comparing the total numbers of Naninidae and Helicidae from Sumatra to New Guinea, we obtain this interesting result:—

It will be noticed that the proportion of Naninidae to Helicidae, which has been nearly 4 to 1 in Sumatra, falls to 3 to 1 in Java, and rises again to 4 to 1 in Borneo (showing the essentially continental character of the island); in Celebes it further falls to 3 to 2, while in the Moluccas the scale turns and Helix has the advantage by about 8 to 5, and in N. Guinea by more than 2 to 1.

There is the same absence of marked features of individuality in Celebes as in the islands dealt with above. Not a single genus is peculiar. The nature of the sea bottom between Borneo and Celebes, with its indications of a somewhat broad bridge over an otherwise deep channel of separation, would seem to account for and suggest the true explanation of the facts as they stand. At the same time, there are indications of a certain amount of contrast between N. and S. Celebes. The Indian element, which constitutes the preponderating majority of the fauna, is common to north and south alike. But the north part of the island, in which Obba and Obbina occur, shows decided relationship with the Philippines, while the occurrence of three Chloritis and one Planispira tend to approximate S. Celebes rather with the Moluccas.

The islands eastward of Java, from Bali to Timor Laut and the Tenimber Is., present no trace of individual peculiarities; they simply carry on the Indo-Malay fauna as though along a great peninsula. Even Timor, surrounded as it is on all sides by sea of profound depth, shows no sign of possessing even one peculiar genus. Amphidromus, perhaps the most characteristic of all Indo-Malay genera, occurs throughout, diminishing in numbers as we go eastward (Bali, Lombok, and Sumbawa 4 sp., Timor 2 sp., Timor Laut 1 sp.), while Plectotropis reaches no farther than Flores and Timor. The tubed operculates are altogether wanting. In Timor Laut we have Moluccan influence appearing in 3 Chloritis, and there is one (supposed) Corasia. Two Helices of a marked Australian type (Rhagada) occur, one in Flores, the other on Dama I., south-west of Timor. The configuration of the sea bottom (see map) would lead us to believe that the north-west coast of Australia once stretched a good deal nearer to these islands.

The Moluccas, taken as a whole, constitute a transition region between the Indo-Malay and the Papuan faunas, uniting, to a very considerable extent, the features of both. They fall into two well-defined groups. The northern, or Ternate group, consists of Gilolo (Halmahera), Batchian, and the outlying islands as far south as and including Obi major. The southern, or Amboyna group, consists of Buru, Ceram, Amboyna, and the chain of islands to the south-east of Ceram, as far as, and including the Ké Is.

The Ternate group shows decidedly closer relations with New Guinea than the Amboyna group. Thus, among the Helices, the markedly Papuan genus Papuina is represented by 7 species in the Ternate group, but by 1 in the Amboyna group. Again, the Cristigibba section of Planispira, which is a Papuan form, has 4 representatives in the northern group, but only 1 in the southern. Certain points of connexion with Celebes come out in the southern group which are wanting in the northern; thus of Chloritis there are 8 species in Amboyna, 0 in Ternate, 3 in Celebes.

In the Moluccas the Helicidae, for the first time as we move eastward from India, gain the ascendancy over the Naninidae, the numbers being, Helix 55, Nanina 36. If we take the groups separately, we find that in the Amboyna group the proportion is 22 to 23, while in the Ternate group it is 33 to 13, an additional proof that the Amboyna group is far less Papuan than the Ternate. Of Planispira, the most characteristic sub-genus of Helix, there are 12 species in the Ternate group, and 5 in the Amboyna. The section Phania, which contains 4 species of the finest Helices known, is quite peculiar to the Ternate group. One species of Obbina, a sub-genus markedly Philippine, occurs in each group. Several of the Indo-Malay land operculates (e.g. Ditropis) reach their limit here, and here too we have the last Clausilia (strangely absent from the Amboyna group). Amphidromus is not reported on sufficient authority to warrant its insertion in the list.

Land Mollusca of the Moluccas. (T = Ternate, A = Amboyna[370] group)

(d) The Philippine Province.—In the extraordinarily rich development of their Mollusca, the Philippines form a remarkable contrast with the poverty of the adjacent Malay islands. No less than 727 species of land Mollusca alone are known from the group, amongst which are included some of the finest and handsomest forms yet discovered. The main features of the fauna are Indo-Malay, with the addition of a certain Australasian element, and a remarkable development of individual characteristics.

The principal indigenous feature is the profuse abundance of the genus Cochlostyla, a group of large and elegant land shells, partly helicoid, partly bulimoid in shape, many of the species of which are covered with a curious hydrophanous epidermis. They are in the main of arboreal habits, living in the tops of the enormous forests which cover the greater part of the islands. As many as 247 species, belonging to 15 sub-genera, have been described.

The distribution of the sub-genera of Cochlostyla on the different islands of the Philippine group affords important evidence on the geological relation of the islands to one another. Thus we find Orthostylus and Hypselostyla occurring in the central islands and S. Luzon, but not in Mindanao or Mindoro; we find Chrysalis peculiar to Mindoro, Prochilus to Mindoro and the Cuyos, Ptychostyla to Luban, all these being sub-genera of very marked characteristics. Six out of the fifteen sub-genera are entirely absent from Mindanao, although occurring on the islands in the immediate vicinity. The little group Tablas-Romblon-Sibuyan are entirely deficient in certain sub-genera which occur on the islands surrounding them on all sides.[371]

Other forms peculiar to the Philippines are Diaphora, a section of Ennea with a curiously produced mouth, and several sub-genera of the Naninidae (Vitriniconus, Vitrinoidea, Hemitrichia). The great Rhysota here find their metropolis. Another very marked group of Helix is Obbina, 19 of the 25 known species being peculiar.

The Helicidae proper of the Philippines are still held in check, as in the greater part of the Indian region, by the Naninidae. The single Trachia and Plectotropis, and the 2 species each of Plectopylis and Satsuma, indicate affinities with Indo-China. Further important Indian relationships are seen in the great Nanina and Cyclophorus, which here attain almost Indian dimensions; in Kaliella (8 sp.), Sitala (2), Clausilia (1). Among the operculates we still have 1 Alycaeus and 1 Coptochilus. Singularly enough, several Indian genera which occur here are not found in the intervening islands of Borneo, Sumatra, or Java, e.g. Streptaxis, Hypselostoma, Ditropis, Acmella, and Cyathopoma. The curiously tubed Malay operculates, Opisthoporus, etc., fail to reach the Philippines proper, although occurring in Borneo and N. Celebes; one of them reaches Palawan. The strikingly Malay genus Amphidromus reaches Palawan, but no farther (1 sp.), while 2 species reach Mindanao, and one of these penetrates as far as Bohol and S. Leyte. Amongst the slugs, Mariaella occurs again only in the Seychelles, and Tennentia only in Ceylon.

Land and Fresh-water Mollusca of the Philippines

Islands adjacent to the Philippines.—The Philippines are connected with Borneo by two distinct ridges or banks of elevation, which enclose between them the Soo-loo or Mindoro Sea. There can be little doubt that these ridges represent the ancient highway of transit, by which Indo-Malay species passed into the Philippines. The depth of the sea on either side is profound, ranging from an average of about 1000 fathoms west of Palawan to 2550 off the south-west coast of Mindanao.

It appears that the fauna of the Soo-loo ridge is definitely Philippine up to and including Bongao, Sibutu, and Bilatan, the last islands at the Bornean end of the ridge. On these are found two species of Cochlostyla and an Obbina.

The Palawan ridge may also be described as more or less Philippine throughout. One species of Cochlostyla occurs on Balabac, just north of Borneo, and two on Palawan, but these are perhaps counterbalanced by the definitely Indo-Malay Amphidromus and Opisthoporus (1 sp. each). At the northern end of the ridge, on Busuanga and Calamian, the Philippine element predominates.

Representatives of two remarkable groups of Helix (Camaena and Phoenicobius) occur along the Palawan ridge and in Mindoro. The Phoenicobius find their nearest allies in the curious small group known as Obba, from N. Celebes, the Camaena possibly in a type of Helix (Hadra) occurring in New Guinea and N.E. Australia. The only other Helix from the whole of the E. Indies which bears any resemblance to the Phoenicobius group is H. codonodes Pfr., which is peculiar to the Nicobars. A few forms assigned to Camaena also occur in Further India and Siam. It would appear possible, therefore, that these two isolated groups are a sort of survival of a fauna which perhaps had once a much more extended range.

(2) The Chinese Sub-region.—The Chinese Sub-region includes the whole of China from its southern frontier up to and including the basin of the Blue or Yang-tse River, together with the coast district, including Corea, perhaps as far north as Vladivostok, and the outlying islands of Hainan, Formosa, the Loo-Choo and Bonin groups, and Japan to the north of Niphon. It may be divided into two provinces, the Chinese and the Japanese.

(a) The fauna of the Chinese province proper bears, in many respects, strong marks of relationship to that of India and Siam. Thus Streptaxis, Helicarion, Macrochlamys, Kaliella, Sitala, Ariophanta, Rhysota, Hemiplecta, Diplommatina, Opisthoporus, Pterocyclus, Lagochilus, and Alycaeus all occur, especially in Southern China. The two points in which the sub-region bears special marks of individuality are Helix and Clausilia. The sub-genera of Helix which have their metropolis in China are Satsuma, Cathaica, Aegista, Acusta, Euhadra, Plectotropis, and Plectopylis. Sinistral forms (compare Fig. 213) are rather prevalent. In several cases—e.g. Trichia, Gonostoma, Fruticicola—there is a reappearance of forms which appear to belong to well-known European sub-genera. Clausilia here attains a kind of second centre of distribution, and is represented by its finest forms, which belong to several peculiar sub-genera. The carnivorous Mollusca are not abundant, and are represented by Rathouisia (a peculiar genus of naked slug), Ennea, and Streptaxis. In the western provinces Buliminus is abundant in several sub-genera, one of which appears to be the European Napaeus.

There is little which is striking in the operculates, which are most abundant in the south, and appear to be mainly derived from Indian and Siamese sources. The occurrence of Helicina (3 sp.), Omphalotropis (1), Leptopoma (2), and Realia (2), is evidence of some influence from the far East. Heudeia is a very remarkable and quite peculiar form of Helicina with internal plicae, perhaps akin to the Central American Ceres.

Fresh-water genera are exceedingly abundant, especially Melania, Unio, and Anodonta. The occurrence of Mycetopus (a South-American genus) is remarkable. There are several peculiar forms of fresh-water operculates, whose exact position is hardly yet assured.

Land and Fresh-water Mollusca of the Chinese Province

The island of Hainan, in the extreme south of the sub-region, has 40 species of Mollusca, 22 of which are peculiar, but there is no peculiar genus.

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.

Land and Fresh-water Mollusca of New Guinea

Waigiou is practically a part of New Guinea. Twelve genera and twenty species of Mollusca are known, eight of the latter being peculiar. The occurrence of Papuina, Insularia, and Calycia sufficiently attest its Papuan relationship. Two species each of Albersia, Chloritis, and Planispira occur.[372]

The Aru Is. are, as we should expect from their position, and particularly from the configuration of the adjacent sea bottom (see map), markedly Papuan. At the same time they show unmistakable signs of long-continued separation from the parent island, for of their 36 land Mollusca 15, and of their 20 fresh-water Mollusca 9 are peculiar. The Papuan element consists in the presence of Papuina, Albersia, and Cristigibba. Moluccan influence is not absent, for the three Helicina, the Albersia, and one Cyclotus are all Moluccan species. The fresh-water fauna appears to be a mixture of varied elements. The single Segmentina is common to India, the Glaucomya to Malacca and the Philippines, while the single Batissa is also found in New Zealand.

Land and Fresh-water Mollusca of the Aru Islands

The Louisiades, the d’Entrecasteaux, and Trobriand Is., and Woodlark I., are closely related to New Guinea, containing no peculiar genera. Each group, however, contains a considerable proportion of peculiar species, an indication that their separation from New Guinea dates from a very distant period. From the Louisiades are known 34 species in all, 22 of which are peculiar.

The fauna of the Admiralty Is., of New Hanover, and New Ireland is markedly Papuan, without any especial feature of distinction. The Admiralty Is. contain 15 sp. Papuina, 7 Chloritis, 1 Planispira, and 1 Corasia. A single Janella shows relationship with the New Hebrides and with New Zealand. In New Ireland Planispira (which is specially characteristic of W. New Guinea and the Moluccas) has disappeared, but there are 7 Papuina and 6 Chloritis. The essentially Polynesian Partula is present in both groups.

The prominent feature of the Mollusca of the Solomon Is. is the extraordinary development of Papuina, which here culminates in a profusion of species and singularity of form. The genus is arboreal, crawling on the branches and attaching itself to the leaves of trees and underwood. Of the 140 land Pulmonata known from the group, no less than 50, or 36 per cent, are Papuina. Ten species of Corasia occur, but whether the shells so identified are generically identical with those of the Philippines, is not satisfactorily determined. Trochomorpha, with 22 species, here attains its maximum. Chloritis begins to fail, but still has 3 species. Indo-Malay influence still appears, though feebly, in Hemiplecta (3), Xesta (1), and possibly even Macrochlamys (1). The Rhytida, the 3 Hadra, and possibly the Paryphanta represent the Australian element. The growing numbers of Partula (13), the small and inconspicuous land operculates (only 22 in all, with Helicina very prominent), and the almost complete absence of fresh-water bivalves, show signs of strong Polynesian affinities. An especial link with the New Hebrides, New Caledonia, and the Viti Is. is the occurrence of Placostylus (16 sp.). It is very remarkable that this genus should occur in the Solomon Is. and not in New Ireland. The occurrence of Streptaxis, if authentic, is very noteworthy, the nearest species being from the Philippines.

Land and Fresh-water Mollusca of the Solomon Islands

(b) The Queensland Province.—The strip of coast-line from Cape York to the Clarence R. stands apart from the rest of Australia, and is closely connected with New Guinea. There can be little doubt that it has been colonised from the latter country, since an elevation of even 10 fathoms would create (see map) a wide bridge between the two. Many of the genera are quite strange to the rest of Australia. Land operculates are abundant, and of a Papuan type. Several of the characteristic Papuan genera of Helix (Papuina, Chloritis, Planispira) occur, while Hadra attains its maximum. Panda, Pedinogyra, and Thersites are three remarkable groups in a rich Helix fauna. Parmacochlea is a peculiar form akin to Helicarion. The carnivorous Mollusca are represented by Rhytida, Diplomphalus (New Caledonia), and Elaea. One species of Janella, a slug peculiar to this region, occurs. The predominant fresh-water genus is Bulinus (Isidora). Ampullaria and Anodonta are entirely absent from Australia and New Zealand.