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CHAPTER XXII. AN ouTLINE OF THE GEOGRAPHICAL DISTRIBUTION OF MOLLUSCA.

THE Mollusca being for the most part marine, it does not enter into the plan of this work to go into much detail as to their distribution. The orders and families will, however, be passed briefly in review, and all terrestrial and fresh-water groups discussed in somewhat more detail; with the object of showing how far their distribution accords with that of the higher animals, and to what extent the anomalies they present can be explained by peculiarities of organisation and habits. If the views advocated in our fifth chapter are correct, the regions there marked out must apply to all classes of animals; and it will be the task of the students of each group, to work out in detail the causes which have led to any special features of distribution. All I can hope to do here, is to show, generally and tentatively, that such a mode of treatment is possible; and that it is not necessary, as it is certainly not convenient or instructive, to have a distinct set of “Regions” established for each class or order in the Animal and Vegetable Kingdoms. For all the Marine groups I have merely summarised the information contained in Mr. Woodward's Manual of the Mollusca, but in the case of the Land Shells I have consulted the most recent general works, and endeavoured to give an accurate, though doubtless a very incomplete, account of the most interesting facts in their distribution. As their classification is very unsettled, I have followed that of the two latest great works, by Martens and Pfeiffer.

CLAss—CEPHALOPODA.

Order I—DIBRANCHIATA.

FAMILY 1.—ARGONAUTIDAE. “Paper Nautilus.” (1 Genus, 4 Species).

DISTRIBUTION.—Open seas of all warm regions. Two species fossil in Tertiary deposits.

FAMILY 2.—OCTOPODIDAE. “Polypi.” (7 Genera, 60 - Species).

DISTRIBUTION.—Norway to New Zealand, all tropical and temperate seas and coasts.

TAMILY 3.—TEUTHIDAE. “Squids or Sea-pens.” (16 Genera, 102 Species.)

DISTRIBUTION.—Universal, to Greenland; 2 other genera are fossil, in the Lias and Oolite.

FAMILY 4.—SEPIADAE. “Cuttle Fish.” (1 Genus, 30 Species).

DISTRIBUTION.—All seas: 4 other genera are fossil, in Eocene and Miocene deposits.

FAMILY 5.—SPIRULIDAE. (1 Genus, 3 Species).

DISTRIBUTION.—All the warmer seas.

FAMILY 6. — BELEMNITIDAE. Fossil. (6 Genera, 100 Species).

DISTRIBUTION.—Lias to Chalk in Europe, India and North America.

Order II-TETRABRANCHIATA. |FAMILY 7.—NAUTILIDAE (1 Genus, 3 Species, Living; 4 Genera, 300 Species, Fossil).

DISTRIBUTION.—Indian and Pacific Oceans; and the fossil species from the Silurian Period to the Tertiary, in all parts of the world.

FAMILY 8–ORTHOCERATIDAE. Fossil. (8. Genera, 400 Species).

DISTRIBUTION.—Lower Silurian to Lias.

FAMILY 9.—AMMONITIDAE. Fossil. (14 Genera, 1100 - Species). " .

DISTRIBUTION.—Upper Silurian to Chalk. Found at 16,000 feet elevation in the Himalayas.

CLASS.–GASTEROPODA.

Order I—PROSOBRAWCHIATA.

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

DISTRIBUTION.—The Strombidae, 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.—MURICIDAE. (12 Genera, 1000 Species.)

DISTRIBUTION.—All seas, most abundant in the Tropics. Trichotropis is confined to Northern seas; Murea, and Fusus are cosmopolitan. There are about 700 fossil species, ranging from the Oolite to the Miocene and recent formations.

FAMILY 3–BUCCINIDAE (24 Genera, 1100 species)

DISTRIBUTION.—The Buccinidae, 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 ; DolČum inhabits the Mediterranean as well as the Pacific. There are about 350 fossil species, mostly from the Eocene and Miocene beds.

FAMILY 4–CONIDA. (3 Genera, 850 Species)

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.

FAMILY 5.—VOLUTIDAE (5 Genera, 670 Species)

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.—CYPRAEIDAE (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.—NATICIDAE (5 Genera, 270 species)

DISTRIBUTION.—The Naticidae, 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.

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