THE CARBONIFEROUS PERIOD. 177 



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 

 rear 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, 

 ^), with its colonies of delicate cylindrical tubes united at in- 

 tervals by cross-bars; Zaphrentis (fig. 116, rf) with its cup- 

 shaped skeleton and the well-marked depression (or " fossula ") 

 on one side of the calice ; Amplexus (fig. 116, r), with its 

 cylindrical, often irregularly swollen coral and short septa ; 

 Cyathopliyllum (fig. 116, a), sometimes simple, sometimes form- 

 ing great masses of star-like corallites ; and Chcutetes, with its 

 branched stems, and its minute, "tabulate" tubes (fig. 116, /). 

 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 Carbon- 

 iferous 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, De- 

 vonian, and Carboniferous periods, is found to have all but 

 disappeared, and it is never again represented save sporadic- 

 ally and by isolated forms. 



Amongst the Echinoderms, by far the most important forms 

 are the Sea-lilies and the Sea-urchins the former from their 

 great abundance, and the latter from their singular structure; 

 but the little group of the " Pentremites " also requires to be 

 noticed. The Sea-lilies are so abundant in the Carboniferous 

 rocks, that it has been proposed to call the earlier portion of 

 the period the " Age of Crinoids." Vast masses of the lime- 

 stones of the period are " crinoidal, " being more or less ex- 

 tensively composed of the broken columns, and detached plates 



