The Amphibians of the Permian period belong principally to the order of the Labyrinthodonts, which commenced to be represented in the Carboniferous, and has a large development in the Trias.  Under the name, however, of Paloeosiren Beinerti, Professor Geinitz has described an Amphibian from the Lower Permian of Germany, which he believes to be most nearly allied to the existing “Mud-eel” (Siren lacertina) of North America, and therefore to be related to the Newts and Salamanders (Urodela).

[Illustration:  Fig. 138.—­Protorosaurus Speneri, Middle Permian, Thuringia, reduced in size. (After Von Meyer.) [Copied from Dana.]]

Finally, we meet in the Permian deposits with the first undoubted remains of true Reptiles.  These are distinguished, as a class, from the Amphibians, by the fact that they are air-breathers throughout the whole of their life, and therefore are at no time provided with gills; whilst they are exempt from that metamorphosis which all the Amphibia undergo in early life, consequent upon their transition from an aquatic to a more or less purely aerial mode of respiration.  Their skeleton is well ossified; they usually have horny or bony plates, singly or in combination, developed in the skin; and their limbs (when present) are never either in the form of fins or wings, though sometimes capable of acting in either of these capacities, and liable to great modifications of form and structure.  Though there can be no doubt whatever as to the occurrence of genuine Reptiles in deposits of unquestionable Permian age, there is still uncertainty as to the precise number of types which may have existed at this period.  This uncertainty arises partly from the difficulty of deciding in all cases, whether a given bone be truely Labyrinthodont or Reptilian, but more especially from the confusion which exists at present between the Permian and the overlying Triassic deposits.  Thus there are various deposits in different regions which have yielded the remains of Reptiles, and which cannot in the meanwhile be definitely referred either to the Permian series or to the Trias by clear stratigraphical or palaeontological evidence.  All that can be done in such cases is to be guided by the characters of the Reptiles themselves, and to judge by their affinities to remains from known Triassic or Permian rocks to which of these formations the beds containing them should be referred; but it is obvious that this method of procedure is seriously liable to lead to error.  In accordance, however, with this, the only available mode of determination in some cases, the remains of Thecodontosaurus and Palaeosaurus discovered in the dolomitic conglomerates near Bristol will be considered as Triassic, thus leaving Protorosaurus[20] as the principal and most important representative of the Permian Reptiles.[21] The type-species of the genus Protorusaurus is the P.  Speneri(fig.