PORIFERA 127 



Cliona (Monaxonida^). A cosmopolitan genus, which bores into 

 the shells of molluscs and into calcareous rocks. 



Halichondriay the crumb-of-bread sponge (Monaxonida). A com- 

 mon British littoral form, usually of encrusting growth. 



Spongilla (Monaxonida). A member of the family of freshwater 

 sponges mentioned on p. 124. Cosmopolitan. 



Euspongia, the bath sponge (Keratosa). Medit., W. Indies, etc. 



Hippospongia (Keratosa). A sponge of the same kind with a coarser 

 texture due to the inclusion of much foreign matter in its skeleton. 



Oscarella (Myxospongiae). British, has no skeleton. 



^ Orders of Demospongiae : Tetractinellida, with tetraxon spicules (Fig. 

 103); Monaxonida, with monaxons; Keratosa, with spongin skeleton; Myxo- 

 spongiae, without skeleton. 



