ACTINOZOA. 205 



the great division of Tahulata, in which the rudi- 

 mentary condition of the septa is made amends 

 for by the extensive development of the transverse 

 floors, referred to in the name this group bears. 



{fi9' 29-) 



The corallum of the Tahulata is mostly, if not 



always, composite. Among the Milleporidce an 

 abundant C08nench3ri2ia occurs, and the resulting 

 compound structure assumes a massive or folia- 

 ceous aspect. The substance of the corallum is 

 traversed by interspaces which give to its section 

 a somewhat tubular or cellular appearance. In 

 the SeriatopoHdce it is more compact, but here, 

 likewise, the coenenchyma is abundant, present- 

 ing, externally, a tufted or arborescent form. In 

 the Favositidce the corallites have their lamel- 

 lar walls brought into very close apposition, little 

 or no true coenenchyma being observable; while 

 in the Thecidw the septa form by their lateral 

 union the greater portion of the dense spurious 

 coenenchyma, of which their massive corallum is 

 composed. 



The following may be given as definitions of 

 the families of Zoantharia. Those of the Madre- 

 poric forms, founded wholly on characters derived 

 from the corallum, admit readily of being ex- 

 hibited under the guise of an analjrtical table. 



Order ZOANTHAEIA. 



Sub-order i. Z. Malacoderrrbata. 



Family i. Actinid^. 



Corallum not evident. Polypes rarely con- 

 nected by a ccenosarc; in general, locomo- 



