392 



Dr. J. E. Dueidcn on (lie Iic/a(ion.s/iij>s 



B<neden (1S90) and ilcMinricli (IS91) have established that 

 the protccneniic stage in the Zoanthids is hexameral, and 

 snch must also have been the case with the extinct coral ; 

 the nictacncmcs arise in succession within two exocop.lic 



Diagraniiuatic representation of the gTooves and ridges occurring- on tlie 

 external surface of the thecal -wall. The bliick linr-s represient the 

 grrooves, the interveuinp- spaces the ridges. The coral is supposed to 

 have been opened vertically along its convex border, and llattened 

 ciut and viewed from the concave side. The sections have shown 

 that jhe larger septa correspond only wiih alternate grooves; hence 

 new ridges always appear in pairs, n(jt singly. The middle line 

 coiresponds with the small counter septum, the one on each side of 

 this with the sn.all s-epta, one on each side of the counter ,«eptum. 

 New septa have I cen added successively on each side of the counter 

 septum, always nt one region, so that as new members appeared the 

 older have been pushed further away. In the jiresent instance thne 

 principal septa (A, B, (") have ap])eared on each side of the counter 

 septum, between it and the lateial or alar primary .septum. Jn the 

 space between the lateral primary septum on eacli side ai.d tlie dorsal 

 lateral septum four piincipal septa (A, B, C, D) have firisen in 

 succession, in each case in the region immediately beyond the alar or 

 lateral septum. No septa have appeared between the upper lateral 

 primary septa and the main se])tum. Only twelve ridges and twelve 

 grooves continue as far as the apex of the coral, repieienting the 

 primary six septa and their interspaces. 



chambers in Zoanthids, in the coral they appeared succes- 

 sively within four similar chambers. In Zoanthids the 

 incompletion of the directives at one axial extremity and their 

 com|jlt'tion at the other extremity may with good reason be 

 correlated with the usual difference in size between the main 



