What does "trionyx" mean?

Trionyx: 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.