216 BRITISH MARINE ALG. 
it is easily obtained when the tide recedes, and frequently (grow- 
ing in society with it) pretty specimens of Ptilota elegans (Fig. 
187), finely coloured plants of JDelesseria alata (Figs. 116 and 
117), and sometimes Grifithsia setacea (Fig. 192), will reward the 
diligent collector. C. tetricum requires some careful manipulation 
in order to make a good book specimen, for the fronds are densely 
branched and very bushy. Young plants are most easily managed, 
or such as do not exceed in size the one represented at Fig. 198, other- 
Fie. 198. Callithamnion tetricum . 
wise the pretty and tolerably regular branching of the lateral plumules 
cannot be effectively displayed. The magnified branch in our illustration, 
Fig. 199, with its long plumules and awl-shaped ramuli, which are set 
alternately on the upper half of the branchlets, was taken from one of 
the fronds of the plant, which is represented the natural size at Fig. 198. 
The colour of this species is a dark brown-red; the substance is very 
rigid, and the fronds do not adhere very firmly to paper. The favelle are 
mostly in pairs, and are seated near the tips of the terminal pinnz or 
winglets. 'Tetraspores are attached to the ultimate ramuli. I have always 
