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 trachia: they are composed of the same kind of plated spar with the fossil shells of the echini, which is usually of a bluish-grey colour, and very bright where fresh-broken; they are all fricated from the centre to the circumference, and have a cavity in the middle. See Plate CI. fig. 4.

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 seem to be the petrified arms of that singular species of the sea-starfish, called stella arborecens.

They are esteemed very powerful diuretics, and prescribed in nephritic cases with good success; the dose being as much of the powder as will lie on a shilling.