GONIOPORA. 



21 



and shows by its knotted or zigzag arrangement how many septa departed from it, then we 

 know that the reticulum is a product of intramural septal fusions. 



These fossils with the 12 central rays might almost be considered as transition forms 

 towards Forties, having to all appearance only 12 septa; but whenever it can be distinctly 

 seen that a certain number of these septa fork before they reach the wall, I assume that this 

 forking is the vestige of the fusion of the septa characteristic of Goniopora, and that therefore 

 there are more than 12. Cf. the diagrams A and B, and the figure 3 given on Plate X 1 . which 

 will serve as one among many examples. 



The three cycles which were present in the primitive parent fused together according to a 

 regular formula which is seen in the earliest fossil representatives of the genus, and persists to 

 this day, wherever the regular type appears or reappears, though it is frequently secondarily 

 obscured in the specialised calicles. This formula is shown in the accompanying diagram (A) 

 (see e.g. PI. I. 3 ; PI. IV. 9 ; PI. V. 4 ; PI. VI. 9 ; also the fossils, PI. X b . figs. 5 and 7). 



Fig. 1. — Diagrams to elucidate the underlying septal formula A of Goniopora, and 

 B of Porites, to show how the latter may be derived from the former. 



Two of the primaries are seen to be directives, while the remaining four fuse with four of 

 the secondaries. The tertiaries fuse in pairs with the secondaries between them. The larger pali 

 arise at the points of fusion of the septa, but seem to be associated more with the secondaries 

 than with the primaries, for it is to be observed that while the directive primaries usually 

 have no pali, the pair of secondaries which do not fuse with primaries have small pali. 

 Whatever be the explanation, it is a fact which has been frequently noticed in the genus, 

 that the pali seem to be usually associated with the secondaries. It is, however, doubtful 

 whether this is invariably the case. For when the secondaries are feebly developed and the 

 primaries are prominent, the teeth of the latter certainly bend up and supply the place of pali. 



To diagram A I have added diagram B, in which the tertiaries are represented as 

 disappearing. Their final disappearance changes the formula typical of Goniopora into thai of 

 Porites. When I described and figured this latter formula,* I despaired of finding any formula 



» Journ. Linn. Soc, xxvii. (1900) p. 488. 



