90 BRITISH FOSSIL SPONGES. 
Family 5.—Prorosponainpa, Hinde, n. 
Sponges cup- or funnel-shaped. Skeletal mesh apparently consisting of a 
single layer of modified hexactinellid spicules, forming quadrate areas of various 
dimensions. Spicules appear to be embedded in a delicate siliceous membrane. 
This family is proposed to include Protospongia, Salter, Phormosella, Hinde, 
Plectoderma, Hinde, and possibly also some of the forms included under Dictyo- 
phyton, Hall. The structure of the sponge-wall resembles that of the dermal layer 
of some of the Sponges of the next family, but, unlike these, no interior meshwork 
is present. Owing to the imperfect condition of preservation, the nature of the 
sponge-wall is not clearly shown; by some authors the spicules are believed to be 
free from each other, and thus of a Lyssakine character. 
Family 6.—SravropErMipm, Zitt. 
Sponges turbinate, funnel-shaped, cylindrical, rarely branching. Interior 
skeletal mesh irregular, spicular nodes simple or octahedral. Dermal layer of 
cruciform or five-rayed spicules forming a regular or irregular framework ; in the 
interspaces a siliceous membrane of smaller spicules. 
Family 7.—Ventricunitipm, Toulmin Suvith (emend. Zitt.). 
Sponges simple or compound, cup-, funnel- or top-shaped, cylindrical or 
ramose. Wall in meandrous folds. Spicular nodes octahedral. Radial canals 
blind. ‘The outer or under surface of the Sponge with elongate apertures or 
furrows, the inner or upper surface either similar to the lower or with circular 
vents. Dermal layer a cribriform siliceous membrane. Root-appendage of 
fasciculate, siliceous fibres, united by transverse extensions, and without axial 
canals. 
Family 8.—Mmanprosponcipm, Zitt. 
Sponges of variable form, consisting of laminate walls in meandrous folds, 
which anastomose together, frequently forming open tubes. Walls with radiate 
blind canals, or with the ordinary apertures of the mesh. Inter-canal system 
always present. Spicular nodes either simple or octahedral. Dermal layer, when 
present, a continuous cribriform membrane either partially or entirely enclosing the 
anastomosing walls. 
