

20 Coelenterata. 



bellum 3 n. , Pourtalosmilia 1 u., Bafliyactis 2 n., Stephanophyllia 1 n., Theco- 

 psammia 1 n. and Gmnopsammia 2 n. - See Alcock( 1 , 2 ). 



According to Duerdenf 1 ) sections through the tip of the corallum of Lopho- 

 phyllwn proliferum show 6 primary septa separated by 6 interseptal spaces. 

 Subsequent septa were formed within only 4 of the interseptal chambers. The 

 larger septa evidently appeared within the entoccelic chambers of the polyp 

 while the later septa are exosepta. The protosepta are also hexameral in 

 the living Aporosa, Fungacea and Perforata in which their development has 

 been followed, so that the hexameral plan of the primary septa of the Paleozoic 

 LopJt. places it in agreement with recent Madreporarian corals. It is other- 

 wise, however, with the subsequent stages of development. While in modern 

 corals the secondary septa are found within the 6 primary exocoels and 

 become arranged in regular alternating hexameral cycles, the later septa in 

 L. and most other Zaphrentoid corals arise bilaterally within only 4 of the 6 

 primary exocoels and never assume a cyclical arrangement but remain bilateral. 

 In respect of their metaseptal sequence, therefore, modern cyclical corals and 

 L. are widely divergent. In L. the new mesenteries were evidently successively 

 developed within 4 of the primary exoccelic chambers and at only one region 

 in each, viz. - - immediately adjacent to a primary pair of mesenteries. This 

 bears the closest resemblance to the condition found in Zoanthid polyps except 

 that in the latter the new mesenteries arise only in 2 exocoelic chambers. The 

 Rugose corals with a metaseptal sequence at all resembling that of L. cannot 

 be associated with other corals, recent or extinct, in which the metasepta arise 

 within all the primary exocoels, nor with the Cerianthese in which growth is 

 axial. The bilateral Zoanthids, primarily hexameral but with their metacnemic 

 development restricted to 2 exocoelic regions, are, more than any other Antho- 

 zoan type, the modern representatives of the Rugosa. The Zoanthids, like 

 the reef-corals with which they live associated, flourish to-day only in tropical 

 seas ; they would seem to represent an old-fashioned Actiuian type which has 

 been preserved as a result of the habit of forming an incrusting skeleton and 

 often compact colonies. The following scheme indicates the different funda- 

 mental types of metacnemic sequence now known in the Actiniaria and 

 Madreporaria and the position among them of the Rugosa. With the exception 

 of the Ceriantheye all possess a primary hexameral stage consisting of 6 pairs 

 of mesenteries with 6 primary entocoelic chambers and 6 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 (meta- 

 cnemes and metasepta) that the divergences are introduced: (1) the metacnemes 

 arise as unilateral pairs at 1, 3, 7, etc. regions with all the 6 primary exoccels 

 and become arranged in 1, 2, 3 or more cycles: (a) non-skeletal: most Actinians 

 (b) skeleton-forming: most recent Madreporariau Corals; (2) the metacnemes 

 arise as bilateral pairs at only one region within 2 or more of the primary 

 exoccels: (a) non-skeletal: Zoanthids (b) skeleton-forming Lobophyllum and 

 probably other Rugosa; (3) the metacuemes arise as bilateral pairs at one 

 region within one or both of the axial entoccels : (a) non-skeletal - - Ceriauthids 

 (b) skeleton-forming - - Forties, Madrepora. - - See Duerden( 2 ). 



Duerden( 3 ) finds that in most of the polyps of the genus Madrepora only the 

 6 bilateral pairs of primary mesenteries are developed of which 4 pairs are 

 complete and 2 incomplete. On any colony a few enlarged polyps may possess 

 a greater number of mesenteries. The new mesenteries, beyond the primary 

 6 pairs, are added in complete or incomplete bilateral pairs, at only the 2 

 axial extremities, the entoccel of the dorsal and ventral directives. The cyclic 



