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One of the two lower valves of the operculum of a barnacle.

has a wreath of plumelike and often bright-colored gills around its head, and usually an operculum to close the aperture of its tube when it retracts.

bevel gears, are used to transmit motion between shafts that are not parallel. -- Spiral operculum, an operculum whih has spiral lines of growth. -- Spiral shell, any shell in which the whorls form a spiral or helix. -- Spiral spring. See the Note under Spring, n., 4.

Situated below the operculum; pertaining to the suboperculum. -- n.

One of the dorsal plates of the operculum of a cirriped.

amily Turbinidæ, usually having a turbinate shell, pearly on the inside, and a calcareous operculum.

ted shell, composed of many whorls. They have a rounded aperture, and a horny multispiral operculum.

Destitute of an operculum, or cover.

A genus of small spiral fresh-water gastropods having an operculum.