92 BRITISH FOSSIL SPONGES. 
are frequently reduced or absent, form a vertical axis. Spicules merely held in 
position by the soft structures of the Sponge. This sub-order is represented by the 
single genus Astrewospongia, Ferd. Roemer. 
Sub-Order 6.—HerErActINnELLIDz. 
Skeletal-spicules consisting of an indefinite number of rays, varying from six 
to thirty, radiating from a common centre. The body-spicules irregularly 
arranged and held in position by the soft structures of the Sponge. The spicules 
of the dermal layer are interwoven together, and their rays partially or completely 
fused with each other. 
Order [V.—CatcisPoncia. 
Sponges whose skeletal spicules are composed of carbonate of lime. Spicules 
either uniaxial, three-rayed, or four-rayed. They are either regularly arranged to 
form the skeleton, or loosely distributed in the soft tissues, or closely apposed 
together to form anastomosing fibres. Only two families have up to the present 
been definitely recognised in the fossil state. 
Family, PHarerrones, Zitt. 
Skeletal-spicules arranged in the form of solid anastomosing fibres. Canals 
branching irregularly, at times not indicated in the skeleton. Dermal layer 
forming a continuous smooth or corrugated membrane. 
Family, Sycones, Haeckel. 
Skeletal-spicules very regularly arranged to form transverse simple radial 
tubes or chambers, which open into a central cloaca. A distinct dermal and 
cloacal layer present. 
