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FAMILY 8.—PYRAMIDELLIDAE. (10 Genera, 220 Species.)
DISTRIBUTION.—These turreted shells are very widely distributed both in temperate and tropical seas; and most of the genera have also a wide range. There are about 400 extinct species, from so far back as the Lower Silurian to the Pliocene formations.
FAMILY 9.—CERITHIADAE. (5 Genera, 190 Species.)
DISTRIBUTION.—These are marine, estuary, or fresh-water shells, of an elongated spiral form; they have a world-wide distribution, but are most abundant in the Tropics. Potamides (41 sp.), is the only fresh-water genus, and is found in the rivers of Africa, India and China, to North Australia, and California. Another genus is exclusively fossil, and there are about 800 extinct species, ranging from the Trias to the Eocene and recent formations.
FAMILY 10—MELAN IADAE (3 Genera, 410 Species.)
I)ISTRIBUTION.—Fresh-water only: lakes and rivers in warm countries, widely scattered. South Palaearctic and Australian regions, from Spain to New Zealand; South Africa, West Africa, and Madagascar; United States. There are about 50 fossil species, from the Wealden and Eocene to recent formations.
FAMILY 11.-TURRITELLIDAE (5 Genera, 230 Species.)
DISTRIBUTION.—Universal. Caecum is found in north temperate seas only. The other genera are mostly tropical, but some species reach Iceland and Greenland. There are near 300 species fossil, ranging from the Neocomian to the Pliocene formations.
FAMILY 12–LITTORINIDAE. (9 Genera, 310 Species.)
DISTRIBUTION.—The Littorinidae 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, Skened, and most species of Rissoa. are Northern. About 180 species are fossil, ranging from the Permian to the Pliocene formations.
FAMILY 13–PALUDINIDAE (4 Genera, 217 Species)
DISTRIBUTION.—The Paludinidae, or River-snails, are all fresh
water, 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—NERITIDAE (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—TURBINIDAE (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.—HALIOTIDAE. (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–FISSURELLIDAE. (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–CALYPTRAEIDAE (4 Genera, 125 Species).
DISTRIBUTION.—The Calptraeidae, 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.—PATELLIDAE. (4 Genera, 254 Species).
DISTRIBUTION.—The Patellidae, 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–DENTALIADAE. (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—CHITONIDAE. (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—P ULMONIFERA. (“Torrestrial 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 Helicidae 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–HELICIDAE. (33 Genera, 3,332 Species) (1860). GENERAL DISTRIBUTION.—Universal.
The Helicidae, 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—Helia, and Pupa–occurring in all the six regions, while Helia, 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 Palaearctic 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:— Helia (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 Palaearctic region as far as North China and Japan. Isolated from this area is a small group of 4 species occurring