CRISIA. 283 
Mr. Hassall describes it as follows :—“ Cells disposed in 
a double series, armed with a long spinous process; joints 
of an amber-colour; vesicles much resembling a fig in 
shape, and dotted.” Mr. W. W. Saunders says that it is 
not uncommon at Brighton and Hastings; but he consi- 
ders it as the perfect state of Crisia eburnea. 
4, CrislA GENICULATA, J. J. Lister. 
Hab. On littoral alge, Brighton, Lister; on Rytiphlea 
puastroides, Brighton, W. W. Saunders; Strangford Lough, 
W. Thompson; Ayrshire coast, D. L. 
Dr. Johnston states that this differs from Crisia eburnea 
in being more slender and less calcareous ;—in the straight- 
ness of the secondary branches, and in the tubular form of 
the cells, which are alternate and free at the apices. I do 
not think that the specific name given it by Milne Edwards 
is very characteristic, for, as Dr. Johnston states, it is only 
subgeniculate. He thinks that the characters which dis- 
tinguish it from C. ebwrnea are rather those of a variety 
than of a species. I have sometimes thought so too; and 
yet | am, on the whole, disposed to regard it as distinct. 
On the Ayrshire coast C. ebwrnea is found on almost every- 
thing, whereas C. geniculata is scarcely ever seen except 
on Desmarestia aculeata, which is often quite hoary with 
