G. CRISIA, 
59 
TOOTHED. 
2. Ac am arc his dentata . Two teeth on the exter- 
nal side of the cells ; opening toothed. Plate 3, fig. 3. 
a. B. 
Australasia. 
CRISIA. 
Plant-like Polypidom. Dichotomous or branch- 
ing ; cells slightly projecting, alternate, rarely oppo- 
site, with their opening on the same surface. 
All the Crisias have so much analogy of form 
with each other, that these Polypidoms are easily to 
be distinguished. 
Their substance is in general calcareous, with arti- 
culations more or less horny. 
In the dried specimens, the colour slightly varies ; 
it is usually a dirty white, but sometimes quite pure, 
and at others tinged with yellow or violet. Their 
height is generally from four to six centimetres ; in 
sbme species it reaches to a decimetre, but I never 
met with any exceeding that size. 
The Crisias, unlike the Cellarias, which shun the 
Thalassiophytes, exclusively prefer these vegetables, 
which they embellish with their white cretaceous 
tufts : they are found, in the warm and temperate 
regions, at all seasons of the year ; but in the colder 
climates, they are rarely found during winter; and 
their existence in all places appears to depend on 
the marine plant to which they are fixed. 
