FLUSTRIDiE. 113 



This simple type of avicularium is common amongst the 

 members of this genus ■^. 



The aperture is placed above the middle of the cell^ and 

 therefore rather higher up than in C. fistulosa. The cells 

 in the same series are separated by a very considerable 

 space. In the older portions of the zoarium the ridge 

 which traverses it is often inconspicuous or nearly obli- 

 terated ; but it may always be traced in the younger parts 

 of the colony, towards the extremity of the cylindrical 

 internodes. 



Family VII. — Flustridae. 



EscHARiDiE (part.), Johnst. B. Z. : D'Orbigny, Pal. Fran9. 

 Flustrad.e (part.), Busk. 

 FLUSTHIDiE, Smitt. 



ZoARiuM corneous and flexible -^ , expanded ,foliaceous, erect. 

 ZocECiA contiguous, multiserial. Avicularia usually 

 of a very simple type. 



Closely allied to the Membraniporida, the Flustrida 

 are distinguished by their erect, flexible, and frond-like 

 zoaria. The two families are certainly not very sharply 

 defined. In its primary stage, Flustra sometimes takes 

 on the Membraniporidan mode of growth ; whilst, on the 

 other hand, Membranipora in some cases (e. g. M. 

 flustroides and M. cornigera) exhibits the type of avicu- 



* In this less highly specialized form of avicularium all the parts of the 

 cell are distinctly represented. The area with its inclosing walls is present, 

 though reduced in size ; the mandible is simply u.* oral operculum, en- 

 larged, and raised by the hood-like elevation of the beak behind it. 



t A certain amovmt of calcareous matter is combined with the horny 

 substance of the zoarium. 



