Tri*on"yx (?), n. [NL., fr. Gr. (see Tri-) + a claw.] Zool.
A genus of fresh-water or river turtles which have the shell imperfectly developed and covered with a soft leathery skin. They are noted for their agility and rapacity. Called also soft tortoise, soft-shell tortoise, and mud turtle.
⇒ The common American species (Trionyx, ∨ Aspidonectus, ferox) becomes over a foot in length and is very voracious. Similar species are found in Asia and Africa.
© Webster 1913.