12 BRITISH FOSSIL CORALS. 
commonly met with. In the genus Acervularia the distinguishing of so-called paliform 
lobes or enlargements and teeth is sufficiently difficult. 
The number of genera without pali is very considerable. 
Columella—This structure is in the axis of the coral, and may be noticed in the 
centre of the calice or of transverse sections of corallites, whilst in longitudinal 
sections it is to be seen passing from the base upwards, having the pali or septa on 
either side.’ 
The columella is not invariably present, but in some species it forms the most important 
part of the calicular apparatus.” The most highly developed columelle spring from the 
centre of the base of the young corallum, increase in height with the growth of the septa, 
and always appear as prominent organs in the calice. These columella grow mde- 
pendently of the septa, and are not formed by their internal and free terminations. For this 
reason they are called “essential” or “propria; they generally assume the styliform, 
the fasciculate, or the lamellar character, and may or may not have pali attached to 
them.° 
The second kind of columella is termed “ septa/,” and is produced by the inner ends 
of the septa dividing into longitudinal “ poutrelles.” They have a fascicular arrangement. 
These “septal” columella are rare, and may, for all practical purposes, be considered 
with the next kind. 
The third kind of columella is formed by the septa dividing into numerous processes 
before they approach closely ; the processes unite centrally, and throw out lateral growths, 
so that a more or less dense, spongy, or cellular structure results. This columella is 
termed parietal, and may be very highly developed or may be rudimentary. In the 
latter instance the columella may only be recognised by a slight bifurcation of the inner 
ends of the septa, with a sparely developed cross tissue. 
False columelle are formed by the soldering together of the inner ends of two or more 
septa, by the twisting of the inner ends of several septa, and by the presence of endotheca 
close to the septal inner margin. 
Rudimentary columelle are often observed, which cannot be classified with any of the 
above ; they may be formed by a lateral junction of the inner ends of the larger septa, by 
processes connecting them, and by the inner ends becoming clubbed in outline, and more 
or less irregular in their direction. 
There are many modifications of these varieties of columell, but their division into 
essential, septal, parietal, and false, is of great practical value, and they can always be dis- 
tinguished with care. The calicular terminations of the columelle vary in size, projection, 
outline, and arrangement. 
1 Plated, figeso, 6, 10; 18. 2 Plate VII, fig. 12. 
3 Plate I, figs. 5, 6, 8, 10, 12; Plate IX, figs. 3, 6, 10. 
