- Three stages in the development of Trochus, during the process of torsion.
Trochus, shell umbilicated, spire pointed and prominent, British.
This typically consists of two concentric zones, the trochus and cingulum, often separated by a groove or gutter which may be finely ciliated; but in several genera of no close affinity, where it is very oblique to the longitudinal axis of the body, it is represented by a general ciliation of the surface (Taphrocampa, Rattulus, Copeus, Adineta).
2, I) and its allies, the trochus being oval with two median gaps, the cingulum, more delicate, and complete.
In Flosculariaceae the trochus is a horseshoe-shaped ridge deep down in the funnel-shaped disk.