Fig. 201.—Characteristic land Mollusca from the Madeira group: A, Helix (Irus) laciniosa Lowe, Madeira; B, Helix (Hystricella) turricula Lowe, Porto Santo; C, Helix (Iberus) Wollastoni Lowe, Porto Santo; D, Helix (Coronaria) delphinuloides Lowe, Madeira.
The Canaries have about 160 species, only about a dozen of which are not peculiar. As many as 75 of these belong to Helix (the sub-genera being very much the same as in the Madeiran group), and 11 to Patula. There is 1 species of Parmacella (which occurs in this group alone), and 6 of Vitrina, of considerable size. A remarkable slug (Plectrophorus) was described from Teneriffe by Férussac many years ago, but it has never been rediscovered, and is probably mythical, or wrongly assigned. Buliminus (Napaeus) has as many as 28 species, all but one being peculiar, and Ferussacia 7. Cyclostoma has two indigenous species, which, with one Hydrocena and one Craspedopoma, make up the operculate land fauna.
The Azores are comparatively poor in Mollusca, having only 52 species, nearly two-thirds of which are peculiar. Helix has 15 species, Patula 4, and Pupa 8. Ferussacia, so abundant in Madeira and the Canaries, is entirely absent, its place being taken by Napaeus (7 sp.), which is curiously absent from Madeira, but richly represented in the Canaries. There are 7 Vitrina, while the land operculates consist of one each of Craspedopoma and Hydrocena. A singular slug (Plutonia), with an ancyliform internal shell, is said to occur. The group was long believed to possess no fresh-water Mollusca, but two species (one each of Pisidium and Physa) have recently been discovered.
The Cape Verdes, owing to the extreme dryness of their climate, are poor in land Mollusca. There are 11 Helix, nearly all of which belong to the group Leptaxis, which is common to Madeira and the Canaries. Ferussacia is absent, Buliminus is represented by a single species, and there are no land operculates. Ethiopian influence, however, as might be expected from the situation of the group, is seen in the occurrence of an Ennea, a Melania, and an Isidora.
It will be noticed how little countenance the molluscan fauna of these island groups gives to any theory of an Atlantis, any theory which regards the islands as the remains of a western continent now sunk beneath the ocean. Had ‘Atlantis’ ever existed, we should have expected to find a considerable proportion of the Mollusca common to all the groups, and perhaps to Europe as well, and there would apparently be no reason why a genus which occurred in one group should not occur in all. As a fact, we find the species extremely localised throughout, and genera occur and fail to occur in a particular group without any obvious reason. All the evidence tends to show that the islands are purely oceanic, and have been colonised from the western coasts of the Mediterranean, i.e. from the direction of the prevailing currents and winds.
(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.