vosites_ which are such a striking feature
in the Devonian limestones, are represented but by one or two
degenerate and puny successors. On the other hand, we meet in
the Carboniferous rocks not only with entirely new genera--such
as _Axophyllum, Lophophyllum_, and _Londsdaleia_--but we have an
enormous expansion of certain types which had just begun to exist
in the preceding period. This is especially well seen in the Case
of the genus _Lithostrotion_ (fig. 116, b), which more than any
other may be considered as the predominant Carboniferous group of
Corals. All the species of _Lithostrotion_ are compound, consisting
either of bundles of loosely-approximated cylindrical stems, or of
similar "coral-lites" closely aggregated together into astraeiform
colonies, and rendered polygonal by mutual pressure. This genus
has a historical interest, as having been noticed as early as in
the year 1699 by Edward Lhwyd; and it is geologically important
from its wide distribution in the Carboniferous rocks of both the
Old and New Worlds. Many species are known, and whole beds of
limestone are often found to be composed of little else than
the skeletons of these ancient corals, still standing upright
as they grew. Hardly less characteristic of the Carboniferous
than the above is the great group of simple "cup-corals," of
which _Clisiophyllum_ is the central type. Amongst types which
commenced in the Silurian and Devonian, but which are still well
represented here, may be mentioned _Syringopora_ (fig. 116, e),
with its colonies of delicate cylindrical tubes united at intervals
by cross-bars; _Zaphrentis_ (fig. 116, d), with its cup-shaped
skeleton and the well-marked depression (or "fossula") on one side
of the calice; _Amplexus_ (fig. 116, c), with its cylindrical,
often irregularly swollen coral and short septa; _Cyathophyllum_
(fig. 116, a), sometimes simple, sometimes forming great masses
of star-like corallites; and _Choetetes_, with its branched stems,
and its minute, "tabulate" tubes (fig. 116, f). The above,
together with other and hardly less characteristic forms, combine
to constitute a coral-fauna which is not only in itself perfectly
distinctive, but which is of especial interest, from the fact that
almost all the varied types of which it is composed disappeared
utterly before the close of the Carboniferous period. In the
first marine sediments of a calcareous nature which succeeded to
the Coal-measures (the magnesian limes