114 FLUSTRnXE. 



larium which is usual (though not universal) amongst 

 the Flustridee* '. 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. 



Der. Flustrian (Saxon), to weave. 



ESCHARA (part), Pallas : Linn. Syst. ed. 10. 



FLUSTRA, sp., Linnaeus : Lamk. : Johnst. (part.) : Busk : Smitt (part.), &c. 



CHARTELLA, Gray (for F. papyracea, &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 occupying 

 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 zooecium 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 with 

 lateral avieularia resembling those of Scrupoceltaria. 



