GONIOPOEA. 



These different relationships are illustrated in the following scheme. 



29 



A primitive porous Coral, that is, a parent form in which the epithecal cup, or the prototheca, is 

 flattened out and the secondary theca is built of septa joined by synapticulse 



I 



Simple and 

 simply Branching Forms, 



THE EUPSAMMIID-E. 

 [1 Including Turbinaria.] 



Luxuriantly Branching 



Forms, owing to early budding 



and consequent dwarfing of 



the polyps, but with rapid 



growth in height of theca, 



THE MADREP0RID.2E. 

 [? Excluding Turbinaria.] 



Astraeiform Colonies, 



due to early budding while 



the skeleton is incomplete, 



basal and disk-shaped, 



THE P0RITID.E. 



GONIOPORA. 



By suppression of tertiary 

 septa, 



PORITES. 



An objection might be raised to this scheme in that Astraeiform colonies are the 

 simplest kind possible, involving mere budding round the rim. How is it then that the 

 Perforata only evolved such colonies as a secondary process, viz. from the fixation of rudimen- 

 tary, immature skeletons, when, in most other groups, it was probably the very first kind of 

 colony to be formed ? The answer is simple. The true perforate wall only arose when the 

 epitheca was flattened out, and this was brought about by the septa rising high enough to form 

 a secondary theca above the rim of the primitive epithecal cup.* Tall, conical calicles, such 

 as those which necessarily result from budding above the base, could not form Astraeiform 

 colonies. In order to produce them, therefore, the typical perforate calicle, with its tall septal 

 theca, had to be reduced in height, and this was brought about in the way described. 



There are a few other perforate genera besides those above mentioned whose positions have 

 been studied in connection with this genus. The important tertiary fossil Arceacis, which 

 Milne-Edwards and Haime placed among their Madreporaria Aporosa, shows no fundamental 

 difference in structure from the recent Madreporid Astrceopora. 



Actinacis D'Orb. is a cretaceous and early tertiary representative of the Madreporaria 

 perforata of unknown affinities. Eeuss described three lobate branching forms of which the 

 surfaces were well preserved. These are so remarkable that one hesitates before endeavouring 

 to assign the genus any definite place. There is in the National Museum a small collection of 

 early tertiary forms from Kressenberg in Bavaria, the sections of which seem to form a series 

 connecting the genus with Goniopora. But more evidence is necessary than that based simply 

 upon sections which are of very inferior morphological importance as compared with the 

 character of the surface that one hesitates on this account alone definitely to associate the 



* Cf. the series of diagrams, Journ. Linn. Soc, xxvii. (1899) p. 135. 



