Land Mollusca of the Queensland Province

(c) The Melanesian Province includes those islands on which the remarkable group Placostylus occurs, the metropolis of whose distribution is New Caledonia. These islands are very possibly the remains of what was once a much wider extent of land. A single species of Placostylus occurs both on Lord Howe’s I. and in the North I. of New Zealand, but this fact, while highly interesting as indicating a possible former extension of land in a south-easterly direction, is hardly sufficient to bring these islands within the province as now limited. The Solomon Is., although containing Placostylus as far to the west as Faro I., form, as has been already stated, a transitional district to the Papuan province.

New Caledonia.—The chief features of the Mollusca are the remarkable development of the helicoid carnivorous genera Rhytida (30 sp.) and Diplomphalus (13 sp.), and of Placostylus (45 sp.). There is a stray Papuina, and a peculiar form Pseudopartula, but Helix has almost entirely disappeared. Polynesian influence is represented by Microcystis (3 sp.), the so-called Patula (13 sp., many of which are probably Charopa), Tornatellina (2 sp.), and Helicina (20 sp.). Partula does not reach so far south, but there are two species of Janella. The recurrence of Melanopsis (19 sp.), absent from the whole Oriental region, is curious, and forms another link with New Zealand. The curious sinistral Limnaea (Isidora), common with Australia and New Zealand, is abundant.

The New Hebrides link New Caledonia and the Solomons by their possession of the typical heavy Placostylus (5 sp.) of the former, and the lighter and more elegant Charis (2 sp.) of the latter. There are 4 Papuina, and Partula is abundant (18 sp.), but there is no evidence at present that the carnivorous genera or the Melanopsis and Isidora of New Caledonia occur.

The Fiji Is., by the possession of 14 Placostylus of the Charis section, which is entirely absent from the adjacent Tonga group, form the eastern limit of the province. There appears to be only a single Partula, but the Polynesian element, especially as seen in Navicella (8 sp.), Neritina (20 sp.), Helicina (11 sp.), and Omphalotropis (11 sp.), is very strong. The Microcystis (9 sp.) and Trochomorpha (14 sp.) are also of a Polynesian type.

(2) The Australian Sub-region includes the whole of Australia (with the exception of the Queensland province) and Tasmania, with New Zealand and the off-lying islands. The fauna, from the prevalence of desert, is scanty, especially in genera. Land operculates are almost entirely wanting. Limax is not indigenous, though several species have become naturalised. The bulk of the fresh-water species belong to Isidora, and it is doubtful whether Physa occurs at all. Unio has a few species, and also Vivipara, but neither Anodonta nor Ampullaria occur. There are a few Melania and Neritina.

Tropical South Australia.—The Mollusca are scanty, and occur chiefly in the neighbourhood of the rivers, the soil being arid, with no shelter either of trees or rocks. Fresh-water species predominate, and the rich land fauna of Queensland is totally wanting. There are no land operculates, 6 Hadra, 1 Bulimus (?), 1 Stenogyra.

West Australia.—Owing to the deserts which bound it, the Mollusca are very isolated, only one species being common with N., S., and E. Australia. The chief characteristics are Liparus, a form intermediate between Helix and Bulimus, and, among the Helices, the group Rhagada. There are no slugs, no carnivorous snails, and only three land operculates.

Land Mollusca of West Australia

In Eastern and Southern Australia (New South Wales, Victoria, and South Australia) the tropical element, so abundant in Queensland, almost entirely disappears, the last operculate (a Helicina) only reaching Port Macquarie, though several species of Helicarion occur in the extreme south. Hadra is still abundant in New South Wales (18 sp.) and S. Australia (10 sp.), but becomes scarce in Victoria (2 sp.); New South Wales has also one Panda and two Thersites. Cystopelta is common with Tasmania, and one of the Janellidae (Aneitea) with Queensland. The carnivorous snails are represented by Rhytida. Caryodes, a bulimoid group perhaps akin to Liparus, is common with Tasmania only.

Tasmania.—About 80 species of land Mollusca are known, not more than 10 being common with Australia. No land operculates occur; Endodonta and Charopa are rare, and Hadra has entirely disappeared, but Pupa and Succinea occur. Carnivorous genera are represented by Paryphanta, Rhytida, and Rhenea. Anoglypta is a peculiar section of Helix, while Caryodes, Cystopelta, and Helicarion are common with Australia. Among the fresh-water Mollusca are a Gundlachia (see p. 345), and some forms of Amnicola or Hydrobia, one of which (Potamopyrgus) is common only with New Zealand.[373]

The Neozealanian Province.—The Mollusca of New Zealand, with the Kermadec, Chatham, and Auckland Is., are remarkably isolated. Such genera as Nanina, Partula, Pupa, Stenogyra, Succinea, Vaginula, Truncatella, Helicina, and Navicella, which might have been expected to occur, are entirely absent. The bulk of the land Mollusca are small and obscure forms, perhaps remains of a very early type, and appear to belong to the Zonitidae, neither Patula nor Helix occurring at all. The carnivorous forms are represented by Schizoglossa, a peculiar genus akin to Daudebardia, by Paryphanta, an extraordinary group of large shells with a thick leathery epidermis, and by Rhytida and Rhenea. In spite of its extreme isolation, the general relations of the fauna are partly with New Caledonia, partly with E. Australia. The occurrence of Placostylus has already been mentioned (p. 323), and three species of Janella, a genus which also occurs in Queensland and New Caledonia, indicate the same affinity. Otoconcha is peculiar. The fresh-water Mollusca, besides the Isidora characteristic of the sub-region, are partly related to New Caledonia through the occurrence of Melanopsis, partly to Tasmania through Potamopyrgus, while the peculiar Latia is possibly akin to Gundlachia (Tasmania). The land operculates number only 5 genera and 14 species in all, excluding a doubtful Diplommatina.[374]

Land and Fresh-water Mollusca of the Neozealanian Province

Lord Howe’s I. is remarkable as containing a Placostylus, which thus links the island with this province. The remainder of the fauna is Polynesian, with the exception of a species (common to the Fijis) of Parmella, a slug akin to Helicarion, Parmacochlea, and Cystopelta.

(3) The Polynesian Sub-region includes all the island groups of the central and southern Pacific (except those classified in the Papuan and Australian sub-regions), from the Pelews and Carolines in the west to the Marquesas and Paumotus in the east, and from the Tonga group in the south to the Sandwich Is. in the north. It may be subdivided into (a) the Polynesian province proper, and (b) the Hawaiian province, which includes the Sandwich Is. only.

(a) The general features of the Polynesian province are very similar throughout, although the Mollusca of each island group are in the main peculiar. The species are mostly small and obscure. Helix scarcely occurs, its place being taken by small Zonitidae (Microcystis, Charopa, Trochomorpha, etc.), and by groups of so-called Patula (Endodonta, Pitys, etc.), the exact position of which is not yet settled. Libera, remarkable for its method of ovipositing (p. 128), is peculiar to the Society and Hervey Is.; Partula is almost universal, attaining its maximum (40 sp.) in the Society Is.; Tornatellina, Pupa, and Vertigo occur throughout.

The land operculates consist chiefly of Omphalotropis, Pupina, Realia, and Helicina. Diplommatina and Palaina are abundant on the Pelews, and a Moussonia occurs in the Samoa Is. Ostodes, a small form of Cyclophorus, is found in some of the southern groups. The fresh-water operculates are Melania, Neritina (including Clithon, a sub-genus furnished with spines), and Navicella; there are no Unionidae, while fresh-water Pulmonata are very scarce.

(b) The land Mollusca of the Hawaiian province are distinguished by the possession of four entirely peculiar genera—Achatinella, Leptachatina, Carelia, and Auriculella. More than 300 of the two former genera have been described, every mountain valley of some of the islands having its own peculiar species. The destruction of the indigenous herbage by goats is rapidly extinguishing many forms. Partula, and the small land operculates, so characteristic of the other groups, are, with the exception of Helicina, entirely wanting. The occurrence of one of the Merope group of Helix (Solomon Is.) is remarkable, and there is a rich development of Succinea. “Patula,” Microcystis, Tornatellina, and the other small Polynesian land Pulmonata are well represented. The presence of Isidora, absent from the central Pacific groups, is remarkable, and Erinna is a peculiar genus belonging to the Limnaeidae.