INTRODUCTION. 17 
The endothecal dissepiments, greatly developed in some genera,’ are either rudimentary 
or quite absent in others ;? they are nearly horizontal, inclined and nearly vertical in 
different species, and they may be concave or convex upwards ; moreover, they may either 
be very numerous in each interlocular space or but one or two only may exist. 
As a rule, there is no exact correspondence in all the interloculi as regards the dis- 
tance of the last dissepiment from the upper septal margin. In some species the distance 
is considerable, whilst in others the dissepiments fill in the interloculi close up to the 
bottom of the calicular base. 
The dissepiment is attached to the septum on either side of the interlocular space 
and to the inside of the wall. Its imner edge is either free or joins another dissepi- 
ment, which, not reaching the wall, is carried inward in its growing course, and so with 
other dissepiments in succession. It results that, according to the convexity and size of 
the dissepiments, they produce more or less cellular or vesicular divisions® in the interloculi. 
The dissepiments may be very coarse or the reverse, and in some species they are 
found of several sizes. The distance between the dissepiments varies, and the cellular 
condition of the outer part of the interloculi is often very marked. The straight dissepi- 
ments do not produce the vesicular appearance. Dissepiments often form a vesicular 
tissue when tabule exist. There are some important genera without dissepiments, 
and whose species contain individuals whose internal base forms the lower margin of the 
visceral and interlocular cavities. 
In some species, a filling-up of the interior of the corallum by a process of thickening 
of the lower part of the wall and base supplies the place of the endotheca.* 
The second variety of endotheca, the ¢asu/ar, is recognised by the horizontal direction 
of the processes,” and by each process being on the same level with regard to the inter- 
septal loculi. In fact, the ¢abwle give the idea of passing through septa and everything 
else in their horizontal course, for they appear to shut out all the space beneath them most 
perfectly. Their extent varies with the diameter of the corallite, and is influenced by the 
occasional presence of vesicular endotheca® near the wail ; but, as a rule, they are attached 
to the inside of the wall and to the septa: they may be distant or very close, very delicate 
or very strong, and they are often marked either by depressions or elevations on their 
upper surfaces. Some tabula are not quite horizontal, but curve upwards in the long 
axis of the corallite, aud others are inclined between horizontal series. 
In Avopora Fisheri (nobis) the great fasciculate columella clearly passes through the 
tabula, and in the genus Colwmnaria the large tabule may be broken off the septa, in 
longitudinal sections, and it may be readily observed that the septa are continuous and 
that the tabulz are not their foundation. 
1 Plate V, fig. 3; Plate I, figs. 15, 18. 2 Plate I, figs. 3, 5, 14. 
3 Plate I, fig. 15. 4 Noticed in many West Indian Tertiary corals. 
5 Plate III, figs. 9, 10, 11. 6 Plate IV, fig. 2; Plate III, fig. 16. 
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