Glossary of Morphological and Anatomical Terms
halteroid spines - Long, straight, external hollow spines, symmetrically developed as strutlike supports on productide ventral valve.
hamiform - Crura straight, in plane of commissure and slightly compressed; variant of falciform crura.
haptoid - Phase of loop development with anterior fusion of ascending and descending elements and their accompanying separation from the vertical plate or septal pillar.
height - In biconvex planoconvex and convexoplane shells, height equals thickness being the maximum dimension normal to length and width in concavoconvex and convexoconcave shells, height is maximum distance measured normal to length in plane of symmetry between shell and line joining beak and anterior margin.Fig.283.
helicophores - See crura.
hemiperipheral growth - New shell material added anteriorly and laterally but not posteriorly.Fig.284.
hemispondylium - Two small plates within thecideoid ventral umbo usually free of valve floor and side walls but commonly supported by median septum and bearing median adductor muscles.
hemisyrinx - Conical chamber extending medially along floor of clitambonitoid spondylium and delineated posteriorly by pair of discrete lateral ridges.
hemisyrinx ridge - Ridge forming posterolateral boundary of hemisyrinx.
hemithyrid stage - See impunctate.
henidium - Symphytium that loses line of junction during late stages of growth.
hinge - Often used loosely for either hinge line or cardinal margin.
hinge area - See cardinal area.
hinge axis - Line joining points of articulation about which valves rotate when opening and closing.Fig.285.
hinge line - Straight posterior margin of shell parallel with hinge axis previously used as synonym of cardinal margin.Fig.285.
hinge notch - Notch at lateral margin of pentameroid delthyrium accommodating posterior side only of hinge tooth.
hinge plate - Medially undifferentiated plate between crural bases.
hinge platform - Solid secondary shell platform extending between socket ridges of terebratellide cardinalia.Fig.370.
hinge projections - Projections of fused inner socket ridges and crural bases visible externally posterior to dorsal umbo.
hinge socket - See dental socket.
hinge teeth - Two principal articulating processes situated at anterolateral margins of delthyrium and articulating with dental sockets in dorsal valve.Fig.322.
hinge trough - See septalium (in sessile form).
hinge width - Lateral extent of hinge line.
holcothyrid stage - See paraplicate.
holoperipheral growth - Increase in valve size all around margins, in posterior as well as anterior and lateral directions.Fig.284.
homeochilidium - Externally convex triangular plate closing almost all or only apical part of notothyrium in paterinides; spelled homoeochilidium by.
homeodeltidium - Externally convex triangular plate closing almost all or only apical part of delthyrium in paterinides; spelled homoeodeltidium by some authors.Fig.286.
hood - Conical structure arising at posteroventral edge of septal pillar or vertical plate on echmidium representing rudiment of ascending elements of loop.
hypothyrid - Pedicle opening located below or on dorsal side of beak ridges with umbo intact.Fig.318.
