In zoology the siren (Siren lacertina), or "mud-eel" of the Americans, one of the perennibranchiate tailed batrachians, is the type of the family Sirenidae, chiefly distinguished from the Proteidae by the structure of the jaws, which, instead of being beset with small teeth, are covered by a horny sheath like a beak; there are, however, rasp-like teeth on the palate, and a few on the inner side of the lower jaw, inserted on the splenial bone.
This, it then seemed, solved the often-discussed question of the perennibranchiate nature of these) Batrachians.
In Gadow's opinion, the reason why there are only perennibranchiate axolotls in these lakes is obvious.
Three blind cave-forms are known: one terrestrial - T y phlotriton, from North America, and two perennibranchiate - Proteus in Europe and Typhlomolge in North America.
8, of a perennibranchiate urodele (Necturus maculosus = Menobranchus lateralis), fig.