SPONGES 109 



Sometimes these are very numerous, th'e 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.) 



//. canaliculatci) variety jlabelluni (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. 



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 XXXVIII.) 



