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from the East coast of South America. The genera have a somewhat restricted distribution as follows:— Auricula (128 sp.), India, Pacific Islands, Peru and West Indies; Melampus (56 sp.), West Indies and Europe; Carychium (9 sp.), Europe and North America; Plectrotrema (14 sp.), Australia, Malay Islands, China, Cuba; Blaumeria (2 sp.), West Indian and Sandwich Islands. There are many fossil species ranging back to the Eocene formation.
The Aciculidae are small cylindrical shells chiefly found in the West Indian Islands, but with representatives widely scattered over the globe. .
Acicula (5 sp.) is European only; Geomelania (21 sp.), and Chittya (1 sp.), are confined to the Island of Jamaica; Truncatella (38 sp.), is most abundant in the Antilles, but is also found in some part of each of the six regions, as indicated by the diagram of the family. But few new species have been added to this group.
The Diplommatinidae are minute shells of the Oriental and Australian regions.
Diplommatina (18 sp.) inhabits India to Burmah, and the greater part of the Australian region; the number of species has now been doubled, and one has been discovered in the island of Trinidad; Clostophis (1 sp.), Moulmein; Pawillus (3 sp.), Borneo, Hong Kong, and Loo Choo Islands.
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This extensive group, comprising the largest of the operculated land-shells, is especially characteristic of the Oriental region, which possesses 25 genera, no less than 12 of them being wholly confined to it. The Neotropical region comes next, with 15 genera, 9 of which are peculiar; but a large number of these are confined to the West Indian Islands, South America itself being very poor in this group. The Palaearctic region has 3 peculiar genera; the Ethiopian and Australian 1 each. The Nearctic region has but a single West Indian species in Florida. The distribution of the genera is as follows:–
Peculiar to or characteristic of the Oriental region are, Opisthoporus (11 sp.), Rhiostoma (6 sp.), Alycaeus (39 sp.), Opisthostoma (1 sp.), Hybocistis (3 sp.), Pterocyclos (19 sp.), extending to the Moluccas; Aulopoma (4 sp.), Dermatocera (4 sp.), Leptopoma (54 sp.), extending west to the Seychelles and east to the Moluccas and New Guinea; Cyclophorus (163 sp.), most abundant in the Oriental region, but ranges to Japan, to Chili, and all Tropical America, over the whole Australian region, and to Natal and Madagascar; Cataulus (15 sp.), confined to Ceylon, the Neilgherries and Nicobar Islands; Rhaphaulus (4 sp.), Penang to Ceram; Streptaulus (1 sp.), Arinia (3 sp.), Pupinella (2 sp.), Pupina (24 sp.), half in North India to Philippines and Japan, the other half in Moluccas, New Guinea and Australia; Cyclotopsis (2 sp.), India and Malaya: Registoma (9 sp.), Philippines and Moluccas, New Caledonia and Pacific. - Characteristic of the Neotropical region are:—Cyclotus (111 sp.), half in the Antilles and Tropical America, the rest in the Moluccas, China, Malaya, India, Natal, and the Seychelle Islands; Megalomastoma (27 sp.), abundant in Cuba, West Indies and South America, others in India, Malaya, and Mauritius; Jamaicia (2 sp.), Jamaica; Licina (5 sp.), Antilles; Choanopoma (49 sp.), Antilles; Ctenopoma (25 sp.), Antilles; Diplopoma (1 sp.), Cuba; Adamsiella (15 sp.), Jamaica, Cuba, Guatemala ; Cyclostomus (113 sp.), abundant in Antilles, also occurs in Madagascar, Arabia, Syria, Hungary and New Zealand; Tudora (34 sp.), Antilles, and one species in Algeria; Cistula (40 sp.), Chondropoma (94 sp.), Bourcieria (2 sp.), Tropical America. Peculiar to or characteristic of the Palaearctic region are:— Craspedopoma (5 sp.), confined to Madeira, the Azores and Canaries; Leonia (1 sp.), Spain and Algeria; Pomatias (22 sp.), Europe and Canaries with a species in the Himalayas; Cecina (1 sp.), Manchuria. The Ethiopian region has the pećuliar genus Lithodion (5 sp.), Madagascar, Socotra and Arabia; and Otopoma (19 sp.), Mascarene Islands and Socotra, with a species in Western India and another in New Ireland. The Australian region is characterised by Callia (3 sp.), in Ceram, Australia, and the Philippines respectively; Realia (7 sp.), New Zealand and the Marquesas Islands; Omphalotropis (38 sp.), the Australian region, with some species in India, Malaya, and the Mauritius. The remaining genus, Hydrocena (27 sp.), has a very widely scattered distribution, being found in South Europe, Japan, the Cape, China, Malaya, New Zealand, the Pacific Islands and Chili. From 10 to 20 per cent of new species have been since described in most of the genera of this family.
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The Helicinidae are very characteristic of the Antilles, comparatively few being found in any other part of the world except the Islands of the Pacific. The genera are:– Trochatella (33 sp.), Antilles with a species in Venezuela, and another in Cambodja; Lucidella (5 sp.), Antilles; Helicina (274 sp.), Antilles, Pacific Islands, Tropical America, Southern United States, Moluccas, Australia, Philippines, Java, Andaman Islands and North China; Schasicheila (5 sp.), Mexico, Guatemala and Bahamas; Alcadia (28 sp.), Antilles; Georissa (5 sp.) Moulmein to Burmah. About 10 per cent. of new species appear to have been since described in the larger genera of this
family. General Observations on the Distribution of the Land Mollusca.
A consideration of the distribution of the families and genera of land-shells shows us, that although they possess some special features, yet they agree in many respects with the higher animals in their limitation by great natural barriers, such as oceans, deserts, mountain ranges, and climatal zones. A remarkable point in the distribution of these animals, is the number of genera which have a very limited range, and also the prevalence of genera having species scattered, as it were at random, all over the earth. No less than 14 genera (or about one-sixth of the whole number) are confined to the Antilles, while the greater part of the sub-genera of modern authors are restricted to limited areas.
If we first compare the New World with the Old, we find the difference as regards genera quite as great as in most of the vertebrates. In the Helicidae, 10 genera are confined to the New, and 7 to the Old World, 16 being common to both. In the Operculata the number of genera of restricted range is greater, the New World having 15, the Old World 32 genera, only 8 being common to both. Of the New World genera 12 out of the 15 do not occur at all in South America; and of those of the Old World, 22 out of the 32 occur in a single region only. If we take the northern and southern division proposed by Professor Huxley (the latter comprising the Australian and Neotropical regions), we find a much less well-marked diversity. Among the Helicidae only 4 are exclusively northern, 8 southern ; while among the Operculata 22 are northern, 16 southern. The best way to compare these two kinds of primary division will be to leave out all those genera confined to a single region each, and to take account only of those characteristic of two or more of the combined regions; which will evidently show which division is the most nětural one for this group. The result is as follows:–
GENERA COMMON TO Two or MORE REGIONS IN, AND CONFINED TO, EACH PRIMARY DIVISION OF THE EARTH.
- Helicide - Operculata. Totals.
We find then that the northern and southern division of the globe is not at all supported by the distribution of the terrestrial molluscs. It is indeed very remarkable, that the connection so apparent in many groups between Australia and South America is so scantily indicated here. The only facts supporting it seem to be, the occurrence of Geotrochus (a sub-genus of Helix) in Brazil, as well as in the Austro-Malayan and West Pacific Islands and North Australia; and of Bulimus in the same two parts of the globe, but peculiar sub-genera in each. But in neither case is there any affinity shown between the temperate portions of the two regions, so that we must probably trace this resemblance to some more ancient diffusion of types than that which led to the similarity of plants and insects. Still more curious is the entire