The royal natural history . nd spiral ridges, producinga cancellated surface. The forms are variable; some are oval, others turreted, andthe most remarkable of all (C<i ncellaria irigonostoma) has the spire drawn outlike a cork-screw. A constant feature in this family consists of three or four folds,plaits, or plicae upon the columella. A few of the species are common, but manyare extremely rare. About a hundred different forms are known. They aremostly tropical, but the genus Adraete has a more northern range, extending asfar as Greenland. They are usually obtained in shallow water, but a
The royal natural history . nd spiral ridges, producinga cancellated surface. The forms are variable; some are oval, others turreted, andthe most remarkable of all (C<i ncellaria irigonostoma) has the spire drawn outlike a cork-screw. A constant feature in this family consists of three or four folds,plaits, or plicae upon the columella. A few of the species are common, but manyare extremely rare. About a hundred different forms are known. They aremostly tropical, but the genus Adraete has a more northern range, extending asfar as Greenland. They are usually obtained in shallow water, but a few specimenshave been dredged at a depth of nearly seven hundred fathoms. SECTION EHACHIGLOSSA. This group of Pectinibranchs includes a large number of genera and speciessuperficially very different. They are all marine gastropods, with a well-developedextensile proboscis, sometimes as long as, or even longer than the body, Theradula is generally long, narrow, and armed with three teeth in a transverse row, GASTROPODS. 37,. one central or rhachidian, and one lateral on each side; the latter, however, arewanting in certain groups. The respiratory siphon is rather long, fitting into theanterior canal or notch of the aperture. The eggs of these molluscs are deposited instrong leathery capsules, each capsule often containing a large number of ova. Thegenus Yetus, however, which is viviparous, produces a comparatively small numberof young. All have shells, which in nearly all cases are capable of sheltering theentire animal. The principal families in this group are the Olividce, Harpidce,Marginellidce, Volutidw, Mitridce, Fasciolariidce, Turbinellidce, BvAcinidce,Nassidce, Columbettidce, Muricidos, and Corolliophilidoe. The Olives (Olividce) are mostly cylindrical shells, often beautifully orna-mented with markings of various patterns, and always having a highly glossy orenamelled appearance. The aperture is narrow or notched in front, and thecolumella is not strongly plaited as m
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