Potamian \Po*ta"mi*an\, n. [Gr. ? river.] (Zo["o]l.) A river tortoise; one of a group of tortoises ({Potamites}, or {Trionychoidea}) having a soft shell, webbed feet, and a sharp beak. See {Trionyx}. Trionychoidea \Tri*on`y*choi"de*a\, n. pl. [NL. See {Trionyx}, and {-old}.] (Zo["o]l.) A division of chelonians which comprises Trionyx and allied genera; -- called also {Trionychoides}, and {Trionychina}.