Glossary of Morphological and Anatomical Terms

neanic - Youthful phase, immediately following brephic stage of shell development, at which generic characters of shell begin to be apparent.
nearly straight beak - See beak angles.
nepionic - See brephic.
neural valve - See ventral valve.
node - Thickened junction of rib and lamella frequently accentuated by growth line.
nodus - Point of divergence of branches in mantle canal system.Fig.379.
nonintertext - Type of folding in which sulcus or carina of one valve is opposed by plane valve.
nonstrophic - See astrophic.
norellid stage - See unisulcate.
notodeltidium - Plate completely filling delthyrium formed by fusion of deltidial plates with eventual plugging of pedicle foramen by posterior retreat of junction between pedicle epithelium and outer epithelium.
notothyrial cavity - See notothyrial chamber.
notothyrial chamber - Cavity in umbo of dorsal valve corresponding to delthyrial chamber of ventral valve, bounded laterally by inner socket ridges brachiophore plates (or homologues), or by posterolateral shell walls if brachiophore bases absent.
notothyrial platform - Umbonal thickening of floor of dorsal valve between inner socket ridges brachiophore, or crural plates.Fig.323_4,Fig.329.
notothyrid - Pedicle opening in dorsal valve a condition never completely attained.
notothyrium - Median subtriangular opening bisecting dorsal cardinal area or pseudointerarea.Fig.283.