METAZOA 45 
(i.) Hyalospongiae——~Skeleton of siliceous spicules, which are 
usually sexradiate, isolated, or fused into a trellis-work. 
Usually deep-sea forms. Many fossils. Ex. Hyalonema, 
whose spicules may reach a length of two feet ; Euplec- 
tella, or Venus’s flower-basket. 
(i1.) Spiculispongiae.—sSkeleton absent in a few forms; im 
the great majority consisting of siliceous spicules, 
usually independent, but sometimes articulated together, 
or united by organic material. One of the sub-orders, 
the Myxospongiae, is devoid of skeleton. Ex. Hali- 
sarca, Oscarella. In the Tetractinellidae, one of the 
largest subdivisions, the spicules are to a great extent 
four-rayed. Ex. Geodia, Tetilla. 
(iii.) Cornacuspongiae.—sSkeleton of wniaxile spicules united 
by spongin, or of spongin. Inhabit the sea, brackish or 
Jresh water, Ex. Euspongia, the sponge of commerce ; 
Velinea, Spongilla (the freshwater sponge), ete. 
