in Natural History, a genus of extraneous fossils, usually of about an inch in length, and made up of a number of round joints, which, when separate and loose, are called trochite: They are composed of the same kind of plated spar with the fossil shells of the echini, which is usually of a bluish-gray colour, and very bright where fresh broken; they are all striated from the centre to the circumference, and have a cavity in the middle.

The entrochi are found of all sizes, from that of a pin's head to a finger's length, and the thickness of one's middle finger; and are plainly of marine origin, having often sea-shells adhering to them. They are sometimes known by the name of St Cuthbert's beads, and are usually found in limestone.