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 limestones of the Permian), the great group of the Rugose corals, which flourished so largely throughout the Silurian, Devonian, and Carboniferous periods, is found to have all but disappeared, and it is never again represented save sporadically and by isolated forms.

[Footnote 19:  A singular fossil has been described by Professor Martin Duncan and Mr Jenkins from the Carboniferous rocks under the name of Paloeocoryne, and has been referred to the Hydroid Zoophytes (Corynida).  Doubt, however, has been thrown by other observers on the correctness of this reference.]

[Illustration:  Fig. 117.—­Platycrinus tricontadactylus, Lower Carboniferous.  The left-hand figure shows the calyx, arms, and upper part of the stem; and the figure next this shows the surface of one of the joints of the column.  The right-hand figure shows the proboscis. (After M’Coy.)]

[Illustration:  Fig. 118.—­A, Pentremites pyriformis, side-view of the body ("calyx"); B, The same viewed from below, showing the arrangement of the plates; C, Body of Pentremites conoideus, viewed from above.  Carboniferous.]