_Fishes_ are mainly _Ganoids_,
though there are also remains of a few Cestraciont Sharks. Not
only are the _Ganoids_ still the predominant group of Fishes, but
all the known forms possess the unsymmetrical ("heterocercal")
tail which is so characteristic of the Palaeozoic Ganoids. Most
of the remains of the Permian Fishes have been obtained from the
"Marl-slate" of Durham and the corresponding "Kupfer-schiefer" of
Germany, on the horizon of the Middle Permian; and the principal
genera of the Ganoids are _Paloeoniscus_ and _Platysomus_ (fig.
137).

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