40 THE WORLD OF THE SEA. 
We have forgotten to mention the Acetabulum, they are beauti- 
ful formations, though for a long time we knew but little about 
them. They were regarded by Tournefort as alge, and by Linnzus 
as polypes. They are small, round, thin plates, lixe very flat parasols. 
ALARIA. 
(Alaria fistulosa.) 
They are striated in rays, and more or less like the top of certain 
fungi; for example, that of Agaricus androsaceus. To the centre 
of this round top the stalk upon which it is supported is attached. 
This stalk is very slender, long, and jointed. The rays are hollow 
and thin. Tubes communicate with the great cavity of the 
head ; the whole vegetable forming a single cell. The skin of the 
