Trionyx \Tri*on"yx\, n. [NL., fr. Gr. ? (see Tri-) + ? a claw.]

(Zo["o]l.) 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.

Note: The common American species (Trionyx, or Aspidonectus, ferox) becomes over a foot in length and is very voracious. Similar species are found in Asia and Africa.

Source: Webster's Revised Unabridged Dictionary (1913)