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FAMILY 12.—LITTORINIDÆ. (9 Genera, 310 Species.)
DISTRIBUTION.—The Littorinidæ are mostly found on the coasts in shallow water; as the common Periwinkle (Littorina littorea). They are of world-wide distribution ; but Solarium and Phorus are tropical; while Lacuna, Skenea, and most species of Rissoa are Northern. About 180 species are fossil, ranging from the Permian to the Pliocene formations.
FAMILY 13.—PALUDINIDÆ. (4 Genera, 217 Species.)
DISTRIBUTION.—The Paludinidæ, or River-snails, are all freshwater, and range over the whole world. Paludina (60 sp.), is confined to the Northern Hemisphere; Ampullaria (136 sp.), is tropical ; Amphibola (3 sp.), inhabits New Zealand and the Pacific Islands ; Valvata (18 sp.), North America and Britain. There are 72 fossil species of Paludina and Valvata, in the Wealden formation and more recent fresh-water deposits.
Family 14—NERITIDÆ (10 Genera, 320 Species.) DISTRIBUTION.—All warm seas, ranging north to Norway and the Caspian Sea. Neritina and Navicella inhabit fresh or brackish waters, the latter confined to the countries bordering the Indian Ocean and the islands of the Pacific. There are 80 fossil species, from the Trias, Lias, and Eocene formations down to recent deposits.
FAMILY 15.-TURBINIDÆ. (10 Genera, 425 Species).
DISTRIBUTION.—The genus Trochus (200 sp.) has a world-wide range, but the other genera are mostly tropical, and are most abundant in the Indian and Pacific Oceans. There are more than 900 fossil species, found in all parts of the world, from the Lower Silurian to the Tertiary formations.
FAMILY 16.-HALIOTIDÆ. (6 Genera, 106 Species),
DISTRIBUTION.—The Ear-shells are most abundant in the Indian and Pacific Oceans; some are found on the east coasts of the Atlantic, but there are very few in the West Indies. Ianthina (10 sp.) consists of floating oceanic snails found in the warm parts of the Atlantic. Three other genera are fossil, and there are near 500 fossil species of this family ranging from the Lower Silurian to the Pliocene formations.
FAMILY 17.-FISSURELLIDÆ. (5 Genera, 200 Species).
DISTRIBUTION.—All seas. Puncturella (6 sp.) is confined to Northern and Antarctic seas; Rimula to the Philippines; and Parmophorus (15 sp.) from the Cape of Good Hope to the Philippines and New Zealand. There are about 80 fossil species, ranging from the Carboniferous formation to the deposits of the Glacial epoch.
Family 18.—CALYPTRÆIDÆ. (4 Genera, 125 Species).
DISTRIBUTION. — The Calptræidæ, or Bonnet-Limpets, are found on the coasts of all seas from Norway to Chili and Australia ; but are most abundant within the Tropics. The genera are all widely scattered. There are 75 fossil species, ranging from the Devonian to recent formations.
FAMILY 19.—PATELLIDÆ. (4 Genera, 254 Species).
DISTRIBUTION.—The Patellidæ, or Limpets, are universally distributed, and are as abundant in the temperate as in tropical seas. There are about 100 fossil species, ranging from the Silurian to the Tertiary formations.
FAMILY 20.–DENTALIADÆ. (1 Genus, 50 Species).
DISTRIBUTION.—The genus Dentalium is found in the North Atlantic, Mediterranean, West Indies and India. There are 125 fossil species, found in various formations as far back as the Devonian in Europe and in Chili.
FAMILY 21.-CHITONIDÆ. (1 Genus, 250 Species).
DISTRIBUTION.—On rocky shores in all parts of the world. There are 37 fossil species ranging back to the Silurian period.
Order II.--PULMONIFERA. (“ Terrestrial Molluscs.")
The Land and Fresh-water snails are so important and extensive a group, and their classification has been so carefully studied, that their geographical distribution is a subject of much interest. The range of the genera will therefore be given in some detail. For the Helicidæ I follow the classical work of Albers—Die Helicien, Von Martens' Edition (1860); and for the Operculate families, Pfeiffer's Monographia Pneumonopomorum Viventium, 2nd Supplement, 1865. The number of species is, of course, very considerably increased since these works were published (and the probable amount of the increase I have in most cases indicated), but this does not materially affect the great features of their geographical distribution.
FAMILY 22.-HELICIDÆ. (33 Genera, 3,332 Species) (1860).
The Helicidæ, or Snails, are a group of immense extent and absolutely cosmopolitan in their range, being found in the most barren deserts and on the smallest islands, all over the globe. They reach to near the line of perpetual snow on mountains, and
to the limit of trees or even considerably beyond it, in the Arctic regions ; but they are comparatively very scarce in all cold countries. The Antilles, the Philippine Islands, Equatorial America, and the Mediterranean sub-region are especially rich in this family. Comparatively few of the genera, and those generally small ones, are restricted to single regions; but on the other hand very few are generally distributed, only two-Helix and Pupa-occurring in all the six regions, while Helix alone is truly cosmopolitan, occurring in every sub-region, in every country, and perhaps in every island on the globe.
The Neotropical region is, on the whole, the richest in this family, the continental Equatorial districts producing an abundance of large and handsome species, while the Antilles are pre-eminent for the number of their peculiar forms. This region possesses 22 of the genera, and 6 of them are peculiar.
The Palæárctic region seems to come next in productiveness, but this may be partly owing to its having been so thoroughly explored. It possesses 16 of the genera, and 3 of them are confined to it. The great mass of the species are found in the warm and fertile countries surrounding the Mediterranean Sea.
The Ethiopian region has 13 genera, only one of which is peculiar.
The Australian region has 14 genera, 2 of which are confined to the Pacific Islands. · The Oriental has 15 genera and the Nearctic 12, but in neither case are there any peculiar generic types.
The following is the distribution of the several genera taken in the order of their magnitude:
Helix (1,115 sp.), cosmopolitan. This genus is divided into 88 sub-genera, a number of which have a limited distribution. An immense quantity of species have been recently described, so that the number now exceeds 2,000.
Nanina (290 sp.) is characteristic of the Oriental and Australian regions, over the whole of which it extends, just entering the Palæarctic region as far as North China and Japan. Isolated from this area is a small group of 4 species occurring in West Africa. The number of species in this genus have now been increased to about 400..
Clausilia (272 sp.) is most abundant in Europe, with a few species widely scattered in India, Malaya, China, Japan, Equatorial America, and one in Porto Rico. The described species have been increased to nearly 500.
Bulimulus (210 sp.) is American, and almost exclusively Neotropical, ranging from Montevideo and Chili, to the West Indian Islands, California and Texas; with two sub-genera confined to the Galapagos Islands. About 100 new. species have been described since the issue of the second edition of Dr. Woodward's Manual.
Pupa (210 sp.) abounds most in Europe and the Arctic regions, but has a very wide range, being scattered throughout Africa, continental India, Australia, the Pacific Islands, North America to Greenland, and the Antilles; but it is absent from South America, the Himalayan and Malayan 'sub-regions, China and Japan. An extinct species has occurred abundantly in the carboniferous strata of North America. About 160 additional species have been described...
Bulimus (172 sp.) abounds most in Tropical South America; it is also found from Burmah eastward through Malaya to the Solomon and Fiji Islands; there are also scattered species in Patagonia, St. Vincents, Texas, St. Helena, and New Zealand. More than 100 additional species have been described.
Buliminus (132 sp.) ranges from Central and South Europe over the whole Ethiopian and Oriental regions to North China, and through the Australian to New Zealand ; there is also a single outlying species in the Galapagos Islands. About 50 more species have been described.
Cochlostyla (127 sp.) is almost peculiar to the Philippine Islands, beyond which, are a species in Borneo, one in Java, and two in Australia. Very few new species have been added to this genus.
Achatinella (95 sp.) is absolutely confined to the Sandwich Island group. Recent researches have more than tripled the number of described species.