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An Illustrated and Cross-Referenced Glossary of Malacological and Conchological Terms |
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| by Paul S. Mikkelsen | |||
| Term | Definition |
| UMBONAL | Pertaining to the UMBONES. | |
| UMBONAL ANGLE | In pectinoid shells, the angle of divergence of UMBONAL FOLDS. In other shells, approximate angle of divergence of POSTERODORSAL and ANTERODORSAL parts of longitudinal profile. | |
| UMBONAL CAVITY | Part of the interior of the valve (of bivalves) that lies within the UMBO and under the HINGE PLATE (when present). | |
| UMBONAL DEPRESSION | Small depression at the tip of the UMBO in some Arcacea. | |
| UMBONAL FOLD | In pectinoid shells, the ridge originating at the UMBO and setting off the body of the shell from the AURICLE. | |
| UMBONAL POLE | Point of maximum curvature of longitudinal dorsal profile of valve. See also: UMBO. | |
| UMBONAL RIDGE | A radial ridge that sets off the posterior from the central and anterior slopes of a bivalve shell. See also: UMBO. | |
| UMBONAL SLOPE | The line of greatest CONVEXITY which can be traced from the BEAK to the anterior or posterior ventral corners of the valve of bivalves; see also: CORSELET. | |
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