THE STKUCTUEE OF POEITES. 493 



2. The septa meet and fuse, and always in the ivay sliown, two 

 pairs on each side of a line passing through two opposite septa, 

 the significance of which will be seen presently. 



3. The fusion of septa goes still further, and, in addition to 

 the two pairs, a triplet is formed (fig. 3). PL 35. figs. 5 and 

 6 show these fusions fairly clearly, and probably careful study 

 might make them out on some of the other figures, but they 

 can naturally be best seen in forms in which the upper edges 

 of the septa are nearly on a level with the walls. I have never 

 found any other fusions of septa but these. And here we 

 may note that we obviously have the directive plane in the line 

 passing through this triplet and the columellar tubercle. The 

 calicle is divided into two symmetrical halves ; and whether the 

 two cycles of septa are distinguishable or not in size and 

 development, we can always now ascertain which are the 

 primaries and which the secondaries. 



4 & 5. The septa which are best developed in fig. 1 become 

 usually poorly developed in figs. 4 and 5 (diagr.), and their upper 

 edges are interrupted. A portion, frequently only a granule, 

 shows near the wall, and another portion appears as a palus at 

 the tip of each septum. I propose to call the peripheral portions 

 of the septal edges, the septal granules. Their variations are 

 found to supply new and valuable taxonomic characters. 



In these figures, the spaces between the septal granules and 

 the pali are exaggerated, the figures not being intended to 

 be more than diagrams. 



We now come to the pali, which are so very characteristic 

 of the genus, but on the arrangements of which no light has 

 hitherto been shed. 



The Pali. — These structures, though well shown in one of the 

 earliest figures of Porites *, attracted no attention till Dana 

 described them in his ' Zoophytes ' f- He speaks of an inner and 

 an outer ring of points, and adds that sometimes one of the 

 inner unites with two of the outer to form a V-shaped palus. 

 Since that time, the pali have always been treated as features 

 of taxonomic importance, but nothing could be said about them 

 than that their numbers were 5, 6 or more, and that they 

 were large and prominent or the opposite, and occasionally 

 V-shaped. 



* Ellis & Solander, ' Zoophytes,' 1786, pi. 47. fig. 2. 

 t P. 550. 



