in Natural History, a genus of sidrochita or crustated ferruginous bodies, formed in large and in great part empty cases, including a small quantity of an aqueous fluid.

Of this genus there are only two species: 1. The thick-shelled enhydrus, with black, reddish-brown, and yellow crusts. 2. The thinner-shelled kind, with yellowish-brown and purple crusts; neither of which ferments with aquafortis or gives fire with steel.