FLUSTRA. 345 
also placed a little more posteriorly, An important differ- 
ence, however, between these very similar species consists 
in the reniform pedunculate operculum, which projects in 
front of the mouth of the cell. Although this organ exists 
in a great variety of form in many species of Cedlulariada, 
and is particularly well developed in the common C. reptans, 
T am not aware that it has hitherto received the attention 
it would seem to deserve in the distinction of species. This 
process does not arise from the edge of the cell, but from 
the wall of the cell a little beyond the margin, and it usually 
appears to be tubular at its origin. It assumes various 
forms, some very fantastic, and increases in size as the cell 
becomes older, so that in the older cells at the bottom of 
the branches it almost entirely covers the mouth.” 
Genus XVI. FLUSTRA, Sea-Mats, Linneus. 
Gen. Char. Polypidom plant-like, membranous, frondose or 
crustaceous, formed of cells arranged quincuncially in several 
series, and in one or two layers: cells in juxtaposition, more or 
less quadrangular, flat, with distinct border: the aperture trans- 
verse, semi-lunar, valvular, subterminal.— Dz». Johnston. 
