POLYZOA. 
63 
forms a delicate silvery lace-work, encrusting shells and seaweeds 
(especially red algae) on almost every shore. The long horny spine 
at the base of the membranous area of each cell gives the crust a 
Fig. 11. 
Flustra cribriformis. 
Fig. 12. 
Mectra pilosa. A, incrusting a seaweed, natural size ; B, cells 
magnified ; a, lid or operculum. 
pilose appearance. In Mectra verticillata from West Africa, the cells 
form an elegant branched colony, the branches being composed of 
regular verticils of cells. 
Membranipora membranacea occurs in the form of horny incrusta- Cage A j 
