278 Murray and Boodle . — A structural and 
a large number of the specimens of this species collected by 
Ferguson, we found that the fronds exhibited almost every 
degree of reticulate cohesion between the two types, and 
equally wide variations in the angle of branching, size of ulti- 
mate branches, etc., so that it is hardly possible to make a 
diagnosis to suit all the specimens. 
The branching in the frond of most of Harvey’s specimens 
is rectangular, and the reticulum very perfect ; this is also the 
case in several of Ferguson’s specimens (Fig. 6 b), but in many 
of the latter the cohesion of branches is very imperfect, whole 
pinnae with their pinnules remaining free from one another 
or united only at one or two points. The cohesion evidently 
begins at different times in different individuals, for in some 
the fronds show a reticulate structure when they are still very 
small, but in others the pinnae grow to a considerable length 
before the pinnules become attached, thus producing a frond 
like that in Kiitzing’s figure ; but we are of opinion that these 
forms would, whea older, become like the more reticulate 
forms. The angle of branching is sometimes acute, but 
when the pinnae have become united with one another by 
means of their pinnules, if, as is probable, growth ceases in 
the pinnae in acropetal order, they become straightened out 
so as to stand at right angles to the midrib. The lower parts 
of the frond are often, as in S. macrophylla , more rectangular 
than the upper. 
The specimens of S. delicatula , var. Caracasana (Fig. 7 a ), 
have regularly bipinnate fronds, and the pinnules have only 
become attached in one or two places (Fig. 7 b), but, from 
the mode of attachment, the fronds must be pretty nearly 
mature. 
One very anomalous form (Fig. 8 a) was collected by 
Ferguson ; it has very upright branches, and we should have 
classed it as an oppositely branched Cladophora , but for the 
following facts : — the character of its roots and stalk is exactly 
the same as that of the specimens of the Struvea delicatula , 
with which it is associated, its plan of branching (although 
more upright) is very much the same, and here and there the 
