THE CARBONIFEROUS PERIOD. 73 
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 speczes 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, Chonophylum, Acervularia, Spongophyllum, Smithia, 
Endophyllum, and Cystiphyllum, have now disappeared; and 
the great masses of /avosites 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 Lz¢hostrotion (fig. 116, 6), 
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 astreeiform 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. Manyspecies 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 Clszophyllum 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 in- 
tervals by cross-bars ; Zaphrentis (fig. 116, @), 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 form- 
ing great masses of star-like corallites ; and Chefetes, 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, 
