THE TRIASSIC PERIOD. 221 



or bases directed backwards. Two similar plates in the lower 

 jaw correspond to the upper, their undulated surfaces fitting 

 exactly to those of the opposite teeth. There are also two 

 sharp-edged front teeth, which are placed in the front of the 

 mouth in the upper jaw; but these have not been recognized 

 in the fossil specimens. The living Ceratodus feeds on vege- 

 table matters, which are taken up or torn off from plants by 

 the sharp front teeth, and then partially crushed between the 

 undulated surfaces of the back teeth (Giinther) ; and there 

 need be little doubt but that the Triassic Ceratodi followed 

 a similar mode of existence. From the study of the living 

 Ceratodus, it is certain that the genus belongs to the same 

 group as the existing Mud-fishes (Dipnoi) ; and we therefore 

 learn that this, the highest, group of the entire class of Fishes 

 existed in Triassic times under forms little 01 not at all differ- 

 ent from species now alive ; whilst it has become probable 

 that the order can be traced back into the Devonian period. 



The Amphibians of the Trias all belong to the old order of 



Fig. 147. Ceratodus Foateri, the Australian Mud-fish, reduced In size. 



the Labyrinthodonts, and some of them are remarkable for 

 their gigantic dimensions. They were first known by their 

 footprints, which were found to occur plentifully in the Tri- 

 assic sandstones of Britain and the continent of Europe, and 

 which consisted of a double series of alternately-placed pairs 

 of hand-shaped impressions, the hinder print of each pair being 

 much larger than the one in front (fig. 148). So like were these 

 impressions to the shape of the human hand, that the at that 

 time unknown animal which produced them was at once chris- 

 tened Cheirotherium, or " Hand-beast. " Further discoveries, 

 however, soon showed that the footprints of Cheirotherium 

 were really produced by species of Amphibians which, like the 

 existing Frogs, possessed hind-feet of a much larger size than 



