ENHYDRUS, in natural history, a genus of siderochita or crustated ferruginous bodies, formed in larga and in great part empty cases, inclosing 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 aqua fortis, or gives fire with steel.