Labyrinthodonta, an extinct order of Amphibia (q.v.), of which Archegosaurus in the Coal-measures is perhaps the oldest known, and Labyrinthodon, in the Trias, the most recent. They all possess tails, and some seem to have been serpentiform, and possibly devoid of limbs. Much of the skeleton was cartilaginous, and is therefore unknown to us: the occipital condyles were often permanently so; and in Archegosaurus the notochord persisted, and we have only bony rings in the vertebra; as in a tadpole. A dermal armour of scales occurs in many genera. The name is derived from the labyrinthine involutions of the walls of the teeth in some genera. The large footprints in Triassic rocks formerly known as Cheirotherium are almost certainly those of Labyrinthodon. As the skull is in some cases three feet in length and two feet broad, these animals certainly reached a colossal size.