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CLASS.—GASTEROPODA.

Order 1.-PROSOBRANCHIATA.

FAMILY 1.—STROMBIDÆ. (4 Genera, 86 Species.)

DISTRIBUTION.—The Strombidæ, or Wing-shells, inhabit tropical and warm seas from the Mediterranean to New Zealand ; most abundant in the Indian and Pacific Oceans. There are nearly 200 fossil species, from the Lias to Miocene and recent deposits.

FAMILY 2.-MURICIDÆ. (12 Genera, 1000 Species.) DISTRIBUTION.-All seas, most abundant in the Tropics. Trichotropis is confined to Northern seas; Mures and Fusus are cosmopolitan. There are about 700 fossil species, ranging from the Oolite to the Miocene and recent formations:

FAMILY 3.—BUCCINIDÆ. (24 Genera, 1100 Species.) DISTRIBUTION.—The Buccinidæ, or " Whelks,” range over the whole world, but some of the genera are restricted. Buccinum inhabits the north and south temperate seas; Monoceros the West Coast of America; Cassidaria the Mediterranean; Phos, Harpa, Eburna, and Ricinula, are confined to the Pacific; Dolium inhabits the Mediterranean as well as the Pacific. There are about 350 fossil species, mostly from the Eocene and Miocene beds.

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DISTRIBUTION.—The Cones are universally distributed, but this applies only to the genus Pleurotoma. Conus is tropical and sub-tropical, and Cithara is confined to the Philippine Islands. There are about 460 fossil species, from the Chalk formation to the most recent deposits.

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DISTRIBUTION.—The Volutes are mostly tropical; but a small species of Mitra is found at Greenland, and a Marginella in the Mediterranean. Cymba is confined to the West Coast of Africa and Portugal. Voluta extends south to Cape Horn. There are about 200 fossil species, from the Chalk and Eocene to recent formations.

FAMILY 6.—CYPRÆDÆ. (3 Genera, 200 Species.) DISTRIBUTION.—The well-known Cowries are found all over the world, but they are much more abundant in warm regions. One small species extends to Greenland. There are nearly 100 fossil species, from the Chalk to the Miocene and recent formations.

FAMILY 7.—NATICIDÆ. (5 Genera, 270 species.)

DISTRIBUTION.—The Naticidæ, or Sea-snails, though most abundant in the Tropics, are found also in temperate seas, and far into the Arctic regions. Two other genera are fossil; and there are about 300 extinct species, ranging from the Devonian to the Pliocene formations.

FAMILY 8.-PYRAMIDELLIDÆ. (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.-CERITHIADÆ. (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.—MELANIADÆ. (3 Genera, 410 Species.)

DISTRIBUTION.—Fresh-water only: lakes and rivers in warm countries, widely scattered. South Palearctic 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.—TURRITELLIDÆ. (5 Genera, 230 Species.)

DISTRIBUTION.—- Universal. Cæcum is found in north teinperate 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.-LITTORINIDÆ. (9 Genera, 310 Species.)

DISTRIBUTION.—The Littorinidæ are mostly found on the coasts in shallow water; as the common Periwinkle (Littoring 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-NERITIDE. (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.-CALYPTRÆDÆ. (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.

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