200 HISTORICAL PALAZONTOLOGY. 
of the Middle Permian; and the principal genera of the 
Ganoids are Paleoniscus and Platysomus (fig. 137). 
The Amphibians of the Permian period belong principally 
to the order of the Zadbyrinthodonts, which commenced to be 
represented in the Carboniferous, and has a large development 
in the Trias. Under the name, however, of Paleosiren Beinert., 
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” (Szvenx dacertina) of North 
America, and therefore to be related to the Newts and Sala- 
manders (Urode/a). 
Finally, we meet in the Permian deposits with the first un- 
doubted remains of true Reptiles. These are distinguished, as 
a class, from the Amphibians, by the fact that they are aur- 
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 Amphzbza undergo in early 
life, consequent upon their transition from an aquatic to a 
more or less purely aerial mode of respiration. ‘Their skel- 
eton 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 js or 
wings, though sometimes capable of acting in either of these . 
capacities, and liable to great modifications of form and struc- 
ture. Though there can be no doubt whatever as to the occur- 
rence of genuine Reptiles in deposits of unquestionable Per- 
mian age, there is still uncertainty as to the precise number 
of types which may have existed at this period. This uncer- 
tainty 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 pres- 
ent between the Permian and the overlying Tnassic 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 palzonto- 
logical 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 Per- 
mian 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 accor- 
dance, however, with this, the only available mode of deter- 
mination in some cases, the remains of Zhecodontosaurus and 
Faleosaurus discovered in the dolomitic conglomerates near 
