The types of animal life which are found in this formation are varied,
and although naturally enough they do not excel in number, there are yet
sufficient varieties to show probabilities of the existence of many with
which we are unfamiliar. The highest forms yet found, show an advance as
compared with those from earlier formations, and exhibit amphibian
characteristics intermediate between the two great classes of fishes and
reptiles. Numerous specimens proper to the extinct order of
_labyrinthodontia_ have been arranged into at least a score of genera,
these having been drawn from the coal-measures of Newcastle, Edinburgh,
Kilkenny, Saärbruck, Bavaria, Pennsylvania, and elsewhere. The
_Archegosaurus,_ which we have figured, and the _Anthracosaurus,_ are
forms which appear to have existed in great numbers in the swamps and
lakes of the age. The fish of the period belong almost entirely to the
ancient orders of the ganoids and placoids. Of the ganoids, the great
_megalichthys Hibberti_ ranges throughout the whole of the system.
Wonderful accumulations of fish remains are found at the base of the
system, in the bone-bed of the Bristol coal-field, as well as in a
similar bed at Armagh. Many fishes were armed with powerful conical
teeth, but the majority, like the existing Port Jackson shark, were
possessed of massive palates, suited in some cases for crushing, and in
others for cutting.

[Illustration: FIG. 24.--_Archegosaurus minor_. Coal-measures.]

[Illustration: FIG. 25.--_Psammodus porosus_. Crushing palate of a fish.]

[Illustration: FIG. 26.--_Orthoceras_. Mountain limestone.]

In the mountain limestone we see, of course, the predominance of marine