CLASSIFICATION. 91 



Family 9. — Ccblopttchid^;, Zitt. 



Sponges with flattened or depressed disc-shaped summits supported on short 

 stems. Interior skeleton of thin laminated walls, folded so as to divide the 

 central cavity into radial chambers. Skeletal mesh regular, with relatively large 

 interspaces ; spicular nodes octahedral. Dermal layer of the upper surface a 

 siliceous membrane with alternately arranged coarse and fine cribriform areas. 

 The vents on the summits of the ridges of the under surface, occasionally also 

 on the stem. 



Group. — Lyssakina, Zitt. 



Skeletal- spicules interlaced and either held in position by the fleshy structures 

 of the Sponge, or exceptionally cemented together irregularly and united by 

 siliceous outgrowths. Spicules often peculiarly modified, their nodes always 

 simple. Flesh -spicules of various forms usually present, also anchoring-ropes 

 of elongated spicules. 



Family 1. — Pollakid^, Marshall. 



Skeletal-spicules may be simple hexactinellids or forms greatly modified by 

 the reduction or subdivision of the normal rays, also by the unusual develop- 

 ment of one or more of the rays. A distinct dermal layer present. Flesh- spicules 

 of varied forms. Anchoring-appendage of elongate spicules, either in bundles or 

 extending singly from the body of the Sponge. 



Family 2. — Receptaculitice, Eichwald, pars, emend. Einde. 



Sponges open cup-shaped, turbinate, sub-spherical and conical, free. The distal 

 ray of the skeletal-spicules modified into a rhomboidal or polygonal plate. The 

 spicules disposed so that the outer plates form a smooth surface of regular oblique, 

 curved, or spiral rows, whilst the four transverse rays mark radial and concentric 

 lines beneath the surface. A perforate inner layer present in one genus. 



Sub-Order 5. — Octactinellim;. 



Skeletal-spicules normally of eight rays, six of which are in a horizontal plane, 

 radiating at equal angles from a common centre, whilst the other two rays, which 



