CLASSIFICATION. 89 
Group.—Drctyonina. 
The skeletal-spicules are normal hexactinellids, whose rays are fused together 
by a common siliceous envelope so as to produce a firmly-united meshwork, which, 
when regular, has cubical interspaces. The spicular nodes or centres may be 
either simple or octahedral. A dermal layer of modified six-rayed spicules usually 
present. Flesh-spicules may be present or absent. 
Family 1.—Euvreripa, Zitt. 
Sponges cup-shaped, cylindrical, turbinate, laminate or branching. ‘Skeletal 
mesh regular; the spicular nodes simple. The dermal layer consists of a 
thickening of the exterior layer of the skeletal mesh, occasionally also a delicate 
meshwork extends completely over the surface, and covers the apertures in the 
sponge-wall. The structure of the root-appendage similar to that of the body of 
the Sponge. 
Family 2.—Coscinoporipa, Zitt. 
Sponges cup-shaped, branching, frequently compressed, or with flange-like 
walls extending from a centre. Very numerous, simple, straight, blind, radiate 
canals, which open alternately on both sides of the sponge-wall. Skeletal mesh 
close, and, owing to the numerous canals, irregular. Spicular nodes usually 
simple, but occasionally octahedral. Dermal layer, when present, a cribriform 
membrane. 
Family 3.—Metuitionipa, Zitt. 
Sponges irregularly globular or branching. Walls completely perforated by 
tubular canals, resembling the cells of honeycomb. Spicular nodes simple. Mesh- 
work irregular. Dermal layer, a delicate siliceous meshwork which covers also the 
canal-apertures. 
Family 4.—Cauiopictyonipa, Zitt. 
Sponges cup-, funnel-shaped, or compressed. Spicular mesh large and 
regular ; spicular nodes octahedral. Dermal layer cribriform. No special canals 
shown in skeleton. 
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