The Corals are very numerously represented in the Upper Silurian rocks some of the limestones (such as the Wenlock Limestone) being often largely composed of the skeletons of these animals.  Almost all the known forms of this period belong to the two great divisions of the Rugose and Tabulate corals, the former being represented by species of Zaphrentis, Omphyma, Cystiphyllum, Strombodes, Acervularia, Cyathophyllum, &c.; whilst the latter belong principally to the genera Favosites, Choetetes, Halysites, Syringopora, Heliolites, and Plasmopora.  Amongst the Rugosa, the first appearance of the great and important genus Cyathophyllum, so characteristic of the Palaeozoic period, is to be noted; and amongst the Tabulata we have similarly the first appearance, in force at any rate, of the widely-spread genus Favosites—­the “Honeycomb-corals.”  The “Chain-corals” (Halysites), figured below (fig. 59), are also very common examples of the Tabulate corals during this period, though they occur likewise in the Lower Silurian.

[Illustration:  Fig. 59.—­a, Halysites catenularia, small variety, of the natural size; b, Fragment of a large variety of the same, of the natural size; c, Fragment of limestone with the tubes of Halysites agglomerata, of the natural size; d, Vertical section of two tubes of the same, showing the tabulae, enlarged.  Niagara Limestone (Wenlock), Canada. (Original.)]

[Illustration:  Fig. 60.—­Upper Silurian Star-fishes. 1, Palasterina primoeva, Lower Ludlow; 2, Paloeaster Ruthveni, Lower Ludlow; 3, Paloeocoma Colvini, Lower Ludlow. (After Salter.)]

[Illustration:  Fig. 61.—­A, Protaster Sedgwickii, showing the disc and bases of the arms; B, Portion of an arm, greatly enlarged.  Lower Ludlow. (After Salter.)]

Amongst the Echinodermata, all those orders which have hard parts capable of ready preservation are more or less largely represented.  We have no trace of the Holothurians or Sea-cucumbers; but this is not surprising, as the record of the past is throughout almost silent as to the former existence of these soft-bodied creatures, the scattered plates and spicules in their skin offering a very uncertain chance of preservation in the fossil condition.  The Sea-urchins (Echinoids) are said to be represented by examples of the old genus Paloechinus.  The Star-fishes (Asteroids) and the Brittle-stars (Ophiuroids) are, comparatively speaking, largely represented; the former by species of Palasterina (fig. 60), Paloeaster (fig. 60), Paloeocoma (fig. 60), Petraster, Glyptaster, and Lepidaster—­and the latter by species of Protaster (fig. 61), Paloeodiscus, Acroura, and Eucladia.  The singular Cystideans, or “Globe Crinoids,” with their globular or ovate, tesselated bodies (fig. 46, A, C, D,), are also not uncommon in the Upper