90 BRITISH FOSSIL SPONGES. 



Family 5. — Protospongidjj, 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. — Staurodeemioe, 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. — Ventriculitis, Toulmin Smith (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. — MjEandrospongim], 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. 



