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The most elevated part of a bivalve shell, or the part in which the hinge is situated. Summit level, the highest level of a canal, a railroad, or the like, in surmounting an ascent.

ence, the region where the sun sets; the west. Sunset shell (Zoöl.), a West Indian marine bivalve (Tellina radiata) having a smooth shell marked with radiating bands of varied colors resembling those seen at sunset or before sunrise; -- called also rising sun.

ted above the branchiæ; -- applied especially to the upper division of the gill cavity of bivalve mollusks.

A genus of marine bivalve mollusks having thin, delicate, and often handsomely colored shells.

A genus of long, slender, wormlike bivalve mollusks which bore into submerged wood, such as the piles of wharves, bottoms of ships, etc.; -- called also shipworm. See Shipworm. See Illust. in App.

A genus of very large marine bivalve shells found on the coral reefs of the Indian and Pacific Oceans. One species (T. gigas) often weighs four or five hundred pounds, and is sometimes used for baptismal fonts. Called also paw shell, and fountain shell.

A genus of pearly bivalve shells, numerous extinct species of which are characteristic of the Mesozoic rocks. A few living species exist on the coast of Australia.

Any bivalve shell of the genus Mactra. See Mactra.

One of the siphons of a bivalve mollusk. Capillary tube, a tube of very fine bore. See Capillary. -- Fire tube (Steam Boilers), a tube which forms a flue. -- Tube coral. (Zoöl.) Same as Tubipore. -- Tube foot (Zoöl.), one of the ambulacral suckers of an echinoderm. -- Tube plate, or Tube sheet (Steam Boilers), a fl…

Any bivalve mollusk which secretes a shelly tube around its siphon, as the watering-shell.

A fold of the wall which projects into the cavity of the intestine in bivalve mollusks, certain annelids, starfishes, and some other animals.

One of the lateral prominence just above the hinge of a bivalve shell.

One of the pieces or divisions of bivalve or multivalve shells. Air valve, Ball valve, Check valve, etc. See under Air. Ball, Check, etc. -- Double-beat valve, a kind of balance valve usually consisting of a movable, open-ended, turban-shaped shell provided with two faces of nearly equal diameters, one above another,…

Any larval gastropod or bivalve mollusk in the state when it is furnished with one or two ciliated membranes for swimming.

An extensive tribe of bivalve mollusks of which the genus Venus is the type. The shells are usually oval, or somewhat heartshaped, with a conspicuous lunule. See Venus.

(Zoöl.) (a) A spiral shell having the body whorls rounded or swollen in the middle. (b) A bivalve shell in which the valves are strongly convex.

Any one of numerous species of marine bivalve shells of the genus Venus or family Veneridæ. Many of these shells are large, and ornamented with beautiful frills; others are smooth, glossy, and handsomely colored. Some of the larger species, as the round clam, or quahog, are valued for food. Venus's basin (Bot.), the wi…

- used for watering flowers, paths, etc. (b) (Zoöl.) Any one of several species of marine bivalve shells of the genus Aspergillum, or Brechites. The valves are small, and consolidated with the capacious calcareous tube which incases the entire animal. The tube is closed at the anterior end by a convex disk perforated b…

Any one of numerous species of small marine bivalves belonging to Donax and allied genera in which the shell is wedge-shaped.

Any one of various species of marine bivalve shells belonging to the genus Avicula, in which the hinge border projects like a wing.