106 MARINE INVERTEBRATES 



is bright sulphur-yellow in color, grows in irregular masses of 

 considerable size and fine texture, and has low wart-like promi- 

 nences. It lives on shells spreading over both surfaces, at first 

 forming little burrows, but eventually penetrating the shell in 

 every direction, honeycombing and at last completely destroying 

 it by absorption. Sometimes it settles upon living shells and 

 greatly irritates the animal, which constantly secretes new lime 

 to cover the perforations in its shell. 



These sponges are an important factor in the economy of the 

 sea, as they disintegrate dead shells, which would otherwise 

 accumulate in vast quantities. 



SUBCLASS CALCAREA 



GENUS Grantia 



G. ciliata. Small, urn-shaped or oval, with large aperture at the 

 summit, surrounded by a circle of projecting spicules. It is found in 

 tide-pools and on piles of wharves from Rhode Island northward. 



GENUS Leucosolenia 



L. botryoifles. Tubular, branched. Occurs in the same places as 

 Grantia ciliata. 



SUBCLASS NON-CALCAREA 



GENUS Suberites 



S. compacta. Elongated, compressed masses, sometimes in several 

 lobes; attached by one edge; texture fine, firm, compact; surface 

 smooth ; color bright yellow. It grows on sandy bottoms, and is com- 

 mon in shallow water south of Cape Cod. (Plate XXXVIII.) 



GENUS Polymastia 



P. robusta. When young it forms yellowish-white incrustations 

 over shells and stones ; later it grows into long, slender, round, tapering, 

 finger-like projections. Found on the northern New England coasts in 

 deep water. 



GENUS Cliona 



C. sulphured, the boring-sponge. Irregular massive form of firm 

 texture ; surface covered with scattered low wart-like prominences 

 about one eighth of an inch in diameter ; bright sulphur-yellow. It 

 destroys, by absorption, vast quantities of dea'd shells. 



