68 
SHELL GALLERY. 
or the Silk Coralline, forms delicate brown tufts resembling a 
filamentous alga ; the cells arise separately in a single series from 
Fig. 18. 
Amathia lendigera. A, natural size ; B, magnified. 
the hollow tubular stems and are contracted at their point of 
attachment. 
Nearly all the Ctenostomata are marine, but a few species live 
in fresh water. 
Sub-order 3. — Cyclostomata. 
Case B 2. In the Cyclostomata, which are all calcareous, the usually 
tubular zocecia have plain circular orifices without a lid or frill 
closing over the retracted tentacle-sheath. There are two sections 
in this group, viz., Articulata, in which the cells form branching 
colonies, the branches being connected by horny joints ; and In- 
