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Containing remains of the earliest discovered life of the globe, which included mollusks, radiates and protozoans.

A division of gastropod mollusks having the teeth of the radula arranged in long transverse rows, somewhat like the barbs of a feather.

A class of Mollusca in which the anterior lobes of the foot are developed in the form of broad, thin, winglike organs, with which they swim at near the surface of the sea.

A division of opisthobranchiate mollusks having the branchiæ in a wreath or group around the anal opening, as in the genus Doris.

The chitinous ribbon bearing the teeth of mollusks; -- called also lingual ribbon, and tongue. See Odontophore.

To mollify ; to cause to be less harsh or severe. [Obs.]

One who is engaged in effecting a revolution; a revolutionist. Smollett.

Of or pertaining to the rhachis; as, the rhachidian teeth of a mollusk.

The median part of the radula of a mollusk.

e two tentacle-like organs on the back of the head or neck of a nudibranch or tectibranch mollusk. They are usually retractile, and often transversely furrowed or plicate, and are regarded as olfactory organs. Called also dorsal tentacles. See Illust. under Pygobranchia, and Opisthobranchia.

A division of gastropod mollusks having a large number of long, divergent, hooklike, lingual teeth in each transverse row. It includes the scutibranchs. See Illustration in Appendix.

ornis) having a spine on the nose. -- River limpet (Zoöl.), a fresh-water, air-breathing mollusk of the genus Ancylus, having a limpet-shaped shell. -- River pirate (Zoöl.), the pike. -- River snail (Zoöl.), any species of fresh-water gastropods of Paludina, Melontho, and allied genera. See Pond snail, under Pond.…

The snout of a gastropod mollusk. See Illust. of Littorina.

An extinct order or suborder of bivalve mollusks characteristic of the Cretaceous period; -- called also Rudista. See Illust. under Hippurite.

Boring, or hollowing out, rocks; -- said of certain mollusks which live in holes which they burrow in rocks. See Illust. of Lithodomus.

Any one of numerous species of marine bivalve mollusks of the genus Pecten and allied genera of the family Pectinidæ. The shell is usually radially ribbed, and the edge is therefore often undulated in a characteristic manner. The large adductor muscle of some the species is much used as food. One species (Vola Jacobæus…

A class of marine cephalate Mollusca having a tubular shell open at both ends, a pointed or spadelike foot for burrowing, and many long, slender, prehensile oral tentacles. It includes Dentalium, or the tooth shells, and other similar shells. Called also Prosopocephala, and Solenoconcha.

An order of gastropod Mollusca having a heart with two auricles and one ventricle. The shell may be either spiral or shieldlike.

A genus of oceanic nudibranchiate mollusks having the small branched gills situated on the upper side of four fleshy lateral lobes, and on the median caudal crest.

Any one of the large bivalve mollusks found on the open seacoast, especially those of the family Mactridæ, as the common American species. (Mactra, or Spisula, solidissima); -- called also beach clam, and surf clam.