Chapter III: CAUDATA (19).--Tailed batrachians, with the frontals distinct

from the parietals and the palatines from the maxillary. Some of the
forms breathe by gills throughout their existence, and were formerly
regarded as establishing a passage from the fishes to the
air-breathing batrachians. They are now considered as arrested larvae
descended from the latter. One of the most startling discoveries of
the decade 1890-1900 was the fact that a number of forms are devoid of
both gills and lungs, and breathe merely by the skin and the buccal
mucose membrane (20). Three blind cave-forms are known: one
terrestrial--_Typhlotriton_, from North America, and two
perennibranchiate--_Proteus_ in Europe and _Typhlomolge_ in North
America.

This order contains about 150 species, referred to five families:
HYLAEOBATRACHIDAE, SALAMANDRIDAE, AMPHIUMIDAE, PROTEIDAE, SIRENIDAE.

Fossil remains are few in the Upper Eocene and Miocene of Europe and
the Upper Cretaceous of North America. The oldest Urodele known is
_Hylaeobatrachus_ Dollo (21) from the Lower Wealden of Belgium. At
present this order is confined to the northern hemisphere, with the
exception of two _Spelerpes_ from the Andes of Ecuador and Peru, and a
_Plethodon_ from Argentina.