THE TRIASSIC PERIOD. 215 
with teeth precisely similar to those of its Triassic predecessor ; 
and we thus have become acquainted with the use of these 
Fig. 147.—Ceratodus Fosteri, the Australian Mud-fish, reduced in size. 
structures and the manner in which they were implanted in 
the mouth. ‘The palate carries two of these plates, with their 
longer straight sides turned towards each other, their sharply- 
sinuated sides turned outwards, and their short straight sides 
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 recognised 
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 (Gunther); 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 1s certain that the genus belongs to the same 
group as the existing Mud-fishes (zzz); and we therefore 
learn that this, the highest, group of the entire class of Fishes 
existed in Triassic times under forms little or 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 
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 Chetrotherium, or ‘“‘ Hand-beast.” Further discoveries, 
however, soon showed that the footprints of Cherotherium 
were really produced by species of Amphibians which, like the 
existing Frogs, possessed hind-feet of a much larger size than 
