of the UiKjosd to the Uvnuj ZHintht'(r. .'{OT 



It is quite certain that tlie Rugose corals witli a metaseptal 

 sequence at all resembling that of Lophophi/ltum cannot be 

 associated with other corals, recent or extin-it, in whicli the 

 metasepta arise within all tlie primary exocoeles ; nor can 

 they be placed along with the Cerianthea}, where growth is 

 axi. 1, as was suggested by Lindstro n in 1868. As already 

 pointed out by Neumayr (188')j, the consi derations which 

 induced Qiielch, in his report on the ' Challenger ' reef- 

 building corals, to class the Itugo^a witii modern Aporosa 

 are altogether of secondary importance, and the same must 

 be said of the attempt of Ogilvie (1896). 



Supremacy being accorded the manner of rae-^enterial 

 development as indicating natural relationships, the bilateral 

 Zoanthids, primarily hexameral, but with their metacnemic 

 development restricted to two exocoelic regions, are, more 

 than any other Anthozoan type, the modern representatives 

 of the Rugosa. The Zoanthids, like the reef-corals with whicli 

 they live associated, flourish to-diy only in tropical seas; 

 they would seem to represent an old-fashioned Actinian type 

 whicli has been |)reserved as a result of the habit of forming 

 an incrusting skeleton and often compact colonies. In the 

 past they no doubt bore much the same relationship to the 

 Rugose polyps which the ordinary Actinians of to-day do to 

 the majority of recent corals. 



The following arrangement will best indicate the different 

 fundamental types of metacnemic sequence now known within 

 the Actiniaria and Madreporaria and the position amonu^st 

 them of the Rugosa. With the exception of the Ceriantheai 

 all possess a primary hexameral stage, consisting of six pairs 

 of mesenteries with six primary entocoelic chambers and six 

 primary exocoelic chambers. Calcareous septa may appear 

 within only one or both series of chambers. It is in the 

 succession of the later mesenteries and septa — metacnemes 

 and metasepta — that the divergences are introduced. 



1. The metacnemes arise as unilateral pairs at one, three, seven, kc. 

 regions within all the six primary exocoeles, and become arranged in one, 

 two, thret', or more cycles : 



a. yon-sMetal. b. Skekton-fonnhif/. 



Most Actinian:*. Most recent Madreporarian corals. 



2. The metacnemes arise as bilateral jiairs at only one region within 

 two or more of the primary exocceles : 



a. Kmi-ske'.etaL b. Skeleton- forming. 



Zoanthids. LophophyUum and probably othtn- 



Rugosa. 



3. The metacnemes arise as bilateral pairs at one region within one or 

 both of the axial entocceles : 



a. Kon-skcletnl. b. Skilfton-fonnim/. 



Ceriantliids. Puritcs, Mufh;p<.ra. 



