158 



ACTINOZOA. 



single species. Its, nearest approach, as Milne 

 Edwards has stated, is found in the genus Acervu- 

 laria, which wants, however, synapticulse and 

 columella, the pali, also, being rudimentary. This 

 genus is a member of the extinct order Ru-gosa, 

 in which the sclerodermic corallum may, per- 

 haps, be said to attain its most remarkable deve- 

 lopment. Both septa and tabulae here occur in 

 the same corallite, the former being always ar- 

 ranged in multiples of four. 



Fig. 29. 



COLTJMNAEIA FrANKLINTI. 



Portion of corallum, of the natural size. 



Among the sclerodermic Zoanthavia tabulae 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 synapticulse. In a fourth section, 



