ACTINOZOA. 205 



the great division ©f 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. 



{fiO- 29.) 



The corallum of the Tahulata is mostly, if not 

 always, composite. Among the Mille'poridce an 

 abundant coenenchyma 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 Seriatoporidai it is more compact, but here, 

 like^vise, 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 Thecidce the septa form by their lateral 

 union the greater portion of the dense spurious 

 coenench3rma, 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 analytical table. 



Order ZOANTHARIA. 



Sub-order i. Z, Malacodermata. 



Family i. AcTiNiDyE. 



Corallum not evident. Polypes rarely con- 

 nected by a coenosarc; in general, locomo- 



