344 PALEOZOIC TIME — CARBONIFEROUS AGE. 



and Salamander, and in part, if not altogether, of the tribe of Laby- 

 rinthodonts, having the body covered with scales ; (2) Lacertians, or 

 inferior species of the Lizard tribe ; (3) Swimming Saurians [Enalio-' 

 saurs, or sea-saurians, as the word signifies), allied to the Ichthyosaurs 



case, to those of fishes. The teeth, when set in sockets, never have more than 

 one prong of insertion, while those of Mammals may have two or more. They 

 are of two types, which are so fundamentally distinct that they require the 

 division of the class into two sub-classes. 



I. Amphibians. — Breathing when young (or in the tadpole state) by means of 

 gills, and, with a few exceptions, undergoing a metamorphosis in which they 

 becjinc gill-less. Heart with two cavities, as in Fishes. 



II. True Reptiles. — Having no gills at any period of life, and undergoing 

 no metamorphosis. Heart with three or four cavities. 



I. Amphibians (Batrachia of most authors). 



The Amphibians are the inferior type, and by some zoologists they are re- 

 garded as an independent class, intermediate between Reptiles and Fishes. The 

 skeleton is distinguished by having (1) two occipital condyles for the articula- 

 tion of the head with the body, one placed either side of the foramen ; (2) the 

 ribs very short, or rudimentary, or wanting; (3) the skull flat and usually broad, 

 and of a loose and open structure. The, body in living species is covered with a 

 soft skin, with sometimes minute scales, as in the Cascilians. In an extinct 

 group there are distinct scales; and these species in this and other ways approach 

 the true Reptiles. 



There are three tribes among living species, and a fourth of extinct species, if 

 not also a fifth. 



1. Cascilians, or Snake-like Amphibians. — Body having the form of a snake; 

 no feet. * 



2. Salamandroids, or Batrachia Urodela. — Body usually lizard-like, or re- 

 sembling in form a tadpole; having short legs, as in the Salamanders; some- 

 times, as in Siren, only the two fore-feet developed ; ribs short. They graduate 

 downward into species that keep their gills through life, which, while perfect 

 animals, are representatives of the embryonic or young state of the higher Am- 

 phibians. In others of intermediate grade the gill-opening is retained, but not 

 the gills. But in the large majority the gills and gill-openings both disappear. 



Among the Salamandroids, — 



Some retain their gills through life, as the Sircdon, or Axolntl, of Mexico and 

 western North America, Siren and Nccturus of the United States, and Proteus 

 of the Adelsberg Cave, Carniola. 



Others retain the gill-openings, but not the gills, as Menopoma of the Alle- 

 ghany region. The animals are large, broad, and flat, sometimes over two feet 

 long. The Amphiuma of the Southern States is another example. The jlfcjalo- 

 batrachus (or Sieboldia) is closely related, although the gill-openings become 

 closed up ; it is the largest of the existing tailed Amphibians, having a length 

 exceeding three feet. The fossil Andrias Scheuchzeri is a Tertiary species re- 

 lated to it. 



