INTRODUCTION. , 17 



The endothecal dissepiments, greatly developed in some genera,^ are either rudimentary 

 or quite absent in others ;^ they are nearly horizontalj 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 fiU 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 inner 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 tabulae 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 fiUing-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 oT endotheca, the tabular, is recognised by the horizontal direction 

 of the processes/ and by each process being on the same level Avith regard to the inter- 

 septal loculi. In fact, the tabula 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 wall; 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 tabulae are not quite horizontal, but curve upwards in the long 

 axis of the corallite, and others are inclined between horizontal series. 



In Axopora Fisheri (nobis) the great fasciculate columella clearly passes through the 

 tabulae, and in the genus Columnaria the large tabulae may be broken off the septa, in 

 longitudinal sections, and it may be readily observed that the septa are continuous and 

 that the tabulae are not their foundation. 



1 Plate V, fig. 3 ; Plate I, figs. 15, 18. ^ pia,e I, figs. 3, 5, 14. 



^ Plate I, fig. 15. * Noticed in many West Indian Tertiary corals. 



5 Plate III, figs. 9, 10, 11. « Plate IV, fig. 2; Plate III, fig. 16. 



3 



