Definition of "umbonal" []

• Relating to the umbo. (adjective)

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• "[VENUS CRIBRARI] Shell thick, medium size, slightly ventricose, furnished upon the outside by about twenty-five sharp lamelliform concentric and recurved ribs, crenulated upon the umbonal side; ribbed or ridged transversely on the ventral side, the ridges extending across to the adjacent rib; lunule crenulated."