XIII 



PHYLUM CHORDATA 



245 



FIG. 80S. Pterichthys testudinarius. A, dorsal; B, ventral; C, lateral aspect, c./. caudal 

 fin ; d. f. dorsal fin ; pet. J. pectoral fin. (From the Brit. Mus. Cat. of Fossil Fishes.) 



CLASS IV. AMPHIBIA, 



The Amphibia are distinguished from Fishes by the possession 

 of pentadactyle limbs instead of paired fins, and by the absence of 

 fin-rays in the median fins. They nearly all breathe by gills in 

 the larval condition, and many of them retain those organs 

 throughout life : lungs are, however, usually present in the adult. 

 The class includes the Frogs, Toads, Newts, and Salamanders, as 

 well as the peculiar snake-like Csecilians, and the gigantic extinct 

 Stegocephala or Labyrinthodonts. 



1. EXAMPLE OF THE CLASS.- -THE COMMON FROG (Rana 

 temporaria'), OR THE EDIBLE FROG (Rana esculentci). 



Rana temporaria, is the common British species of Frog, found in 

 ponds and damp situations all over the country ; R. esculenta is the 



