204 HISTORICAL PALAEONTOLOGY. 



belonging to the old genera Orthoceras and Cyrtoceras and the 

 long-lived Nautilus. 



Amongst Vertebrates, we meet in the Permian period not 

 only with the remains of Fishes and Amphibians, but also, for 

 the first time, with true Reptiles. The 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-schief er " of Germany, on the horizon 

 of the Middle Permian ; and the principal genera of the Ganoids 

 are Palaoniscus and Platysomus (fig. 137). 



The Amphibians of the Permian period belong principally 

 to the order of the Labyrinthodonls, 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 Sala- 

 manders (Urodela). 



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 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 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 fins 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 truly Labyrinthodont or Reptilian, 

 but more especially from the confusion which exists at pres- 



