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umbo (pl. umbones) The first part of a brachiopod (Brachiopoda) or bivalve (Bivalvia) shell to be formed. In a brachiopod, the umbo is the posterior part of each valve; in a bivalve it forms the dorsal part of the shell.

umbo

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umbo (pl. umbones) A convex protuberance or swelling in the centre. In Brachiopoda and Bivalvia, the first part of the shell to be formed; it occurs at the posterior of each valve in brachiopods and forms the dorsal part of the shell in bivalves.

umbo

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umbo A convex protuberance or swelling in the centre, as in the pileus of certain fungal fruit bodies.

umbo

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umbo boss of a shield; round or conical projection. XVIII. — L. umbō (see NAVEL).

umbo

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umbo (um-boh) n. a projecting centre of a round surface, especially the projection of the inner surface of the eardrum to which the malleus is attached.