114 FLTJSTRID^. 



larium which is usual (though not universal) amongst 

 the Flustridie^ . Still the general features of the group 

 are sufficiently salient and striking, and its boundary 

 lines probably not more evanescent than those of most 

 of our systematic divisions. 



Genus FLUSTRA^ Linnaus. 



T)ev. Flustrian (Saxon), to weave. 



EscHARA (part.), Pallas : Linn. Syst. eel. 10. 



Flustra, sp., Linnteus : Lamk. : Johnst. (part.) : Busk : Smitt (part.), &c. 



CiiARTELLA, Gray (for F. fcipyracca, &c.). 



Carbasea, Gray: Busk (?part.). 



Semiflustra, sp., D'Orbigny. 



Generic Character. — Zoarium erect, frondose. Zo- 

 (ECiA disposed in a single layer', or in two layers united 

 by the dorsal surfaces, more or less quadrangular or 

 linguiform, with a raised margin, the aperture ocaipying 

 the whole or a considerable portion of the front of the cell, 

 and closed in by a membranous covering. Ocecia im- 

 mersed. 



This genus, as now defined, includes species with two 

 layers of cells, and others with only a single layer. The 

 latter have been detached by some writers, and ranged 

 under the genus Carbasea, Gray; but, so long as the 

 type of the zocecium is the same, it seems to me quite 

 unnecessary to separate the bilamellate and unilamellate 

 forms. It may be a question, perhaps, whether those 

 members of the genus Carbasea, Busk, in which the 

 aperture is reduced to a small opening at the upper ex- 

 tremity of the cell, and the ovicells are external, should 



* The South-African form Carbasea armata, Busk, is furnished witli 

 lateral avicularia resembling those of Scrupocellaria. 



