190 HISTORICAL PALAZONTOLOGY. 
in character to those which occur in the Triassic rocks, and which 
will be subsequently spoken of under the name of Cheirotherium. 
In the Coal-measures of Britain, the continent of Europe, and 
North America, however, many bones of these animals have 
been found, and we are now tolerably well acquainted with a 
considerable number of forms. All of them seem to have be- 
longed to the division of Amphibians in which the long tail 
of the young is permanently retained; and there is evidence 
that some of them kept the gills also throughout life. The 
skull is of the characteristic Amphibian type (fig. 132, a), with 
Fig. 132.—a, Upper surface of the skull of Axthracosaurus Russeliz, one-sixth of the 
natural size; 6, Part of one of the teeth cut across, and highly magnified to show the 
characteristic labyrinthine structure ; ¢, One of the integumentary shields or scales, one- 
half of the natural size. Coal-measures, Northumberland. (After Atthey.) 
two occipital condyles, and having its surface singularly pitted 
and sculptured; and the vertebrz are hollowed out at both 
ends. The lower surface of the body was defended by an 
armour of singular integumentary shields or scales (fig. 132, ¢); 
and an extremely characteristic feature (from which the entire 
group derives its name) is, that the walls of the teeth are deeply 
folded, so as to give rise to an extraordinary “labyrinthine” 
pattern when they are cut across (fig. 132, 4). Many of the 
Carboniferous Labyrinthodonts are of no great size, some of 
