3<5 J. E. DUERDEN. 



peculiarity in the polyp itself, an axial peculiarity situated towards 

 the ventral side. 



In a paper already published (Ann. & Mag. Nat. Hist., May, 

 1902), I have given good reasons for supposing that of all 

 modern Anthozoa the living Zoantheae are most nearly related 

 to the extinct Rugosa. In zoanthids the mesenteries beyond the 

 primary six are added in such a manner as would give the septal 

 sequence characteristic of the Rugosa, that is, the sequence 



FlG. II. A section near the upper limit of the corallite. All the septa are now 

 more strictly radial, and those of the inner and outer cycles regularly alternate. 

 There is no distinction in size between the six protosepta (I) and the various meta- 

 septa (a-e), except as regards the ventral directive septum, the smallness of which 

 gives rise to the simple axial fossula. 



represented in Figs. 2 10 ; the only difference is that in modern 

 zoanthids the new mesenteries are added within only the two 

 ventral of the six primary chambers, whereas in the rugose 

 polyps they were added within four of the six primary chambers 

 the ventral and middle pairs. This difference is, however, 

 but one of detail compared with the actual order of development 



