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A division of opisthobranchiate mollusks, having no shell except while very young. The gills are naked and situated upon the back or sides. See Ceratobranchia.

A genus of extinct Tertiary Foraminifera, having a thin, flat, round shell, containing a large number of small chambers arranged spirally.

the almond, walnut, hickory, beech, filbert, etc.), consisting of a hard and indehiscent shell inclosing a kernel.

A genus of polished marine gastropod shells, chiefly tropical, and often beautifully colored.

Any shell of the genus Oliva and allied genera; -- so called from the form. See Oliva.

he oviduct of certain trematode worms in which the ova are completed and furnished with a shell.

Having an operculum, or an apparatus for protecting the gills; -- said of shells and of fishes.

The lid closing the aperture of various species of shells, as the common whelk. See Illust. of Gastropoda.

cowry (Zoöl.), a large, handsome cowry (Cypræa aurantia), highly valued by collectors of shells on account of its rarity. -- Orange grass (Bot.), an inconspicuous annual American plant (Hypericum Sarothra), having minute, deep yellow flowers. -- Orange oil (Chem.), an oily, terpenelike substance obtained from orange…

A genus of minute living Foraminifera having a globular shell.

A brachiopod shell of the genus Orthis, and allied genera, of the family Orthidæ.

An extinct genus of Paleozoic Cephalopoda, having a long, straight, conical shell. The interior is divided into numerous chambers by transverse septa.

An orthoceras; also, any fossil shell allied to Orthoceras.

The internal bone, or shell, of a cuttlefish.

A division of bivalve mollusks including the oysters and allied shells.

An order of Entomostraca possessing hard bivalve shells. They are of small size, and swim freely about. [Written also Ostracoda.]

Of or pertaining to an oyster, or to a shell; shelly. The crustaceous or ostreaceous body. Cudworth.

ast two forming a couplet. It was used by Byron in "Don Juan," by Keats in "Isabella," by Shelley in "The Witch of Atlas," etc.

d in England for hunting otters. -- Otter sheep. See Ancon sheep, under Ancon. -- Otter shell (Zoöl.), very large bivalve mollusk (Schizothærus Nuttallii) found on the northwest coast of America. It is excellent food, and is extensively used by the Indians. -- Sea otter. (Zoöl.) See in the Vocabulary.…

al species of wading birds of the genus Hæmatopus, which frequent seashores and feed upon shellfish. The European species (H. ostralegus), the common American species (H. palliatus), and the California, or black, oyster catcher (H. Bachmani) are the best known. -- Oyster crab (Zoöl.) a small crab (Pinnotheres ostreum)…