CARBONIFEROUS CORALS AND BRACHIOPODS 113 
possible to arrive at any other conclusion than that the 
separation cannot be upheld. It is also to be remembered 
that both species were founded on the examination of 
specimens derived entirely from England and Ireland. 
In their later work (the Monograph of British Fossil 
Corals, the authors introduce an important distinction 
founded on a supposed difference in the structure of the 
central area, and upon this they seem to place their chief 
reliance. Nothing could be more striking than the differ- 
ence between the two types of structure shown in PI. 33, 
Fig. 36 (a vertical section of C. Murchisoni), and in PI. 33, 
Fig. 4 (a vertical section of C. Stutchburyi) ; but neither 
represents a normal type, common to a large number of 
specimens. The tabuLie are seldom so uniform as in 
Fig. 4, and, amongst the very great number of vertical 
sections which I have seen in collections or had cut from 
specially selected specimens, I have never seen this tabulate 
type continuous throughout the whole section, or, indeed, 
for any considerable distance. The much commoner tabu- 
late type is that in which the tabulae are separated by hori- 
zontal rows of broad horizontal vesicles which, as we proceed 
downwards, become more numerous, until the ordinary 
vesicular structure is reached. Again, Fig. 36 seems to 
be an extreme case of the vesicular type in which tabulae 
are entirely absent (the thick double arches, shown at 
intervals in the figure, seem to correspond to the periodic 
variations in the density of the matrix which are of very 
common occurrence in all types) ; the normal type and the 
one which is to be seen in the great majority of specimens, 
at some point or other of the section, consists in broad 
bands of purely vesicular tissue, more or less horizontally 
arranged, separated at considerable intervals by one or 
more very, short horizontal plates. 
The fact that both structures occur together in the same 
vertical section, and *that the common vesicular type 
