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
belonged 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
two occipital condyles, and having its surface singularly pitted
and sculptured; and the vertebrae 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, c);
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, b). Many of the
Carboniferous Labyrinthodonts are of no great size, some of
them very small, but others attain comparatively gigantic
dimensions, though all fall short in this respect of the huge
examples of this group which occur in the Trias. One of the
largest, and at the same time most characteristic, forms of the
Carboniferous series, is the genus _Anthracosaurus_, the
skull of which is here figured.
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