THE CARBONIFEROUS PERIOD. 173 



of the Carboniferous. Nevertheless, there is an equally decid- 

 ed and striking amount of difference between these successive 

 faunas, due to the fact that the great majority of the Carbon- 

 iferous species are new ; whilst some of the most characteristic 

 Devonian genera have nearly or quite disappeared, and several 

 new genera now make their appearance for the first time. 

 Thus, the characteristic Devonian types Heliophyllum, Pachy- 

 phyllum, Chonophyllum, Acervnlaria, Spongophyllum, Smithia, 

 Endophyllum, and Cystiphyllum, have now disappeared; and 

 the great masses of Favosites 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 predo- 

 minant 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, 

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

 tervals 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. 1 1 6, a}, sometimes simple, sometimes form- 

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

 branched stems, and its minute, ''tabulate" tubes (fig. u6,/). 

 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, 

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