systematic account of the genus Struvea. 277 
an arrangement occurs which reminds one of the branching of 
the main filaments in Ancidyomene . One of the cells is 
club-shaped, and from its swollen end gives off five or seven 
branches of about equal value, though smaller than itself, 
and separated from one another by nearly equal angles. 
The frond appears septate throughout ; a small piece was 
tried, as in S. plumosa, and found to have real transverse walls. 
The tenacula have very well-developed rhizoids, and adhere 
very closely to the filaments. 
5 . tenuis (Fig. 5 a) has a shortly ovate cordate frond with 
5-7 pairs of pinnae, which form a crenate margin by their 
incurved apices, and give off pairs of pinnules, mostly united 
with one another in a very regular manner, the apex of 
one attaching itself to the middle of another (see Fig. 5 b). 
Transverse walls appear to be formed rather late: thus in 
Fig. 5 c there are only one or two present, the other transverse 
marks being slight constrictions. 
The very regular arrangement seen in Fig. 5 b does not 
seem to be constant in this species, for in another specimen 
the mode of attachment varies in different parts of the frond ; 
one pinnule gives off two branches, and some of the pinnules 
attach themselves to the pinnae instead of to each other. A 
very early stage in the formation of the frond is seen in 
Fig. 5 which shows five pairs of protrusions below the apex, 
and below them a constriction, which will probably be the 
point of formation of the septum in the stalk below the frond. 
Although slight creases are seen in one or two places, we 
think there is no doubt that the whole is a single cell. This 
agrees with the late formation of the transverse walls in the 
pinnae. In .S', plumosa the pinnae form their transverse walls 
before giving rise to pinnules, so it is very likely that in the 
formation of the frond cell-walls would precede the branch 
protusions, in that species, as described by Harvey. 
.S. delicatula (Fig. 6 a) is the most variable species of the 
genus. On comparing Kiitzing’s figure of this species with 
Harvey’s figure of his Cladophora ? anastomosans one would 
not be much disposed to unite the two, but in looking through 
