SPONGES 109 
Sometimes these are very numerous, the whole interior being cavernous ; 
again, the structure is more dense, with fewer large openings and more 
of the small ones between the tufts; again, the depressions are 
filled up so that the surface has fewer tufts. When living, the color is 
shining black. This is the best sponge found on the American coast, 
and although of coarser texture than the best Mediterranean sponges, it 
is more durable and quite as elastic. (Plate XL.) 
HT. canaliculata, variety flabellum (Spongia graminea, Hyatt). 
This is one of the species of sponges of the third commercial grade, 
which bear the trade-name of “ grass-sponge.” The shape is cone-like, 
with either a flat or a funnel-shaped top. The oscula .re on the upper 
surface. The sides are fluted with deep furrows which contain the small 
incurrent apertures. 
Genus Hirecinia 
H. campana. The normal variety is vase-shaped, but the species 
varies greatly in form. Some varieties have branches. When living, 
its color is black. It is found at Key West in four to forty feet depth. 
(Plate XX XVIII.) 
