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 brackish and fresh water. 



Sub-order 3. — Cyclostoiviata. 



Case B 2. In the Cyclostomata, which are all calcareous, the usually 



tubular zooecia 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- 



