158 



ACTINOZOA. 



single 



species. Its nearest approach, as Milne 

 Edwards has stated, is found in the genus Acervit- 

 laria, which wants, however, synapticulae and 

 columella, the pali, also, being rudimentar}^ This 

 genus is a member of the extinct order Rugosa, 

 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. 



COLUMNAEIA FEANKI-INn. 



Portion of corallum, of the natural size. 



Among the sclerodermic Zoaiitharia tabulae and 

 septa are scarcely known to co-exist, a special 

 section of this group, Tahulata, being distin- 

 guished by the nearly exclusive possession of the 

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

 the Apovosa 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. 



