An Illustrated and Cross-Referenced Glossary of
Malacological and Conchological Terms

by Paul S. Mikkelsen

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Term Definition

DIAGONAL RIDGE   In bivalves, a ridge running from the UMBO toward posteroventral part of VALVE; see also: CORSELET; DEMARCATION LINE.

ESCUTCHEON RIDGE   Ridge extending posteriorly from beak in each valve (of bivalves) and forming border of ESCUTCHEON; see also: DEMARCATION LINE.

LIGAMENT RIDGE   Narrow ridge or lamina formed by projection of outer layer of shell wall into body cavity of many rudists (particularly hippuritids and radiolitids), thought to have served for attachment of ligament.

POSTERIOR RIDGE   A ridge, in bivalves, passing over or originating near the umbo and running diagonally towards the posteroventral part of the valve; see also: CORSELET.

RESILIAL RIDGE   The point of attachment of the LIGAMENT. See also: RESILIUM.

RIDGE   [need definition].

UMBONAL RIDGE   A radial ridge that sets off the posterior from the central and anterior slopes of a bivalve shell. See also: UMBO.

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