Glossary of Morphological and Anatomical Terms
umbonal angle - See apical angle.
umbonal blade - Part of primary lamella of spiralium extending from lateral branch of jugum to distal end of crus.Fig.336.
umbonal chambers - Pair of posterolaterally located cavities in either valve; in ventral valve bounded by dental plates (cardinal buttresses in trimerelloids) and shell walls; in dorsal valve limited medially by crural plates (or homologues) and shell walls.Fig.351.
umbonal muscle - Single muscle occurring in some lingulides, thought to be homologous with posterior adductors; consists of two bundles of fibers posteriorly and slightly asymmetrically placed.Fig.346_1.
umbonal slopes - Region of shell surface adjacent to umbo.
uniplicate - Form of alternate folding with ventral valve bearing median sulcus and anterior commissure median plica.Fig.289.
unisulcate - Form of alternate folding with dorsal valve bearing median sulcus and anterior commissure median sinus.Fig.289.
