158 



ACTINOZOA. 



single species. Its nearest approach, as Milne 

 Edwards has stated, is found in the genus Acervu- 

 laria, which wants, however, synapticulge and 

 columella, the pali, also, being rudimentary. This 

 genus is a member of the extinct order Rugosci, 

 in which the sclerodermic corallum may, per- 

 haps, be said to attain its most remarkable deve- 

 lopment. Both septa and tabulse here occur in 

 the same corallite, the former being always ar- 

 ranged in multiples of four. 



i 



Fig. 29. 



COLUMNARIA FrANKLINH. 



Portion of corallum, of the natural size. 



Among the sclerodermic Zoantharia tabulse and 

 septa are scarcely known to co-exist, a special 

 section of this group, Tabulata, being distin- 

 guished by the nearly exclusive possession of the 

 former {fig. 29). In two other large divisions, 

 the Aporosa and Perforata, including several 



families, septa, in sets of five or six, normally occur 

 and in some are associated with dissepiments. 

 more rarely with synapticulae. In a fourth section 





