systematic account of the genus Struvea . 269 
incrustation of Acetabularia consists chiefly of calcareous 
algae, just as in the present genus. 
We have seen only one branched specimen in 5. plumosa , 
in which two stalks sprang from a very short common sac-like 
base. In S. macrophylla (Fig. 2 a) the stalk tapers slightly 
from the middle towards each end, is corrugated throughout, 
and resembles that of 6*. plumosa ; and it is presumable that 
the stages of development are the same in the two species, for 
they seem nearly related to one another. 
In 5. ramosa the stalk has a very different appearance from 
that of the two species just mentioned. It is here filiform and 
of about equal diameter throughout, except for a few transverse 
corrugations which occur usually at the base of a stalk, but 
are sometimes absent altogether and would be overlooked at 
the first glance owing to the small diameter of the stalk. 
The stalk is often branched in this species, in which case the 
branches generally show a few corrugations at their bases. 
Branching is generally opposite, Fig. 3 b being a typical ex- 
ample. The branches here are of about equal value, but in 
some specimens the central filament branches again, Before 
the frond is formed the stalk is simply an erect cylindrical 
unicellular tube. Dickie, after describing S. ramosa, , mentions 
the presence of a £ thin, reddish, calcareous coat at the lower 
part’ of the stipes, as one of his reasons for referring it to 
the genus Struvea . This calcareous coat is however, as in 
S. plumosa and S. macrophylla^ evidently due to incrusting algae. 
In S. pulcherrima (Fig. 4 a) the stalk is filiform, cylindrical, 
and smooth (where it is visible, being mostly enveloped by a 
short tufted red sea-weed— no Melobesia being present). It is 
apparently branched into three filaments, each of which is 
again divided into four, but as the whole system bears only 
a single frond, it is better to regard the branches as forming 
the lower part of the frond. In 5'. ramosa the stem was re- 
garded as branched, because each of its divisions bore a per- 
fectly distinct frond ; but taking a single frond of this species, 
it is seen that the filament bearing it divides into three 
branches, which remain simple for a short distance before 
