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, honeyeombing 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. botryoides. 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 XXXVIIL.) 
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. sulphurea, 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 dead shells. 
