M. K. A. ZIttel on Fossil Hexactinellida. 417 



a. Canal-sjstem well-developed. Ostia of the csecal radial 

 canals alternate on the two surfaces. 

 IProtospongia^ Salt. Silurian. 

 Calathium^ Billings. Silurian. 

 Arch(eocyatJius, Billings. Silurian. 

 '^Trachyum, Billings. Silurian. 

 ^ Steganodictyon, M'Coy. Devonian. 

 Tremadictyon, Zitt. Upper Jura. 



Craticularia, Zitt. Middle and Upper Jura, Cretaceous, 

 Miocene. 

 '^Euhrochus^ Sollas. Gault. 

 Sphenaulax^ Zitt. Upper Jura. 

 Sporadojyyle, Zitt. Upper Jura. 

 ^Sclerothamnusj Marsh, f 

 h. Canal-system wanting or scarcely developed. 

 '^Farrea, Bow. Tertiary. 

 '^Eurete^ Marsh. 



Verrucocceh'a. Upper Jura, Cretaceous. 

 ^Aulodictyon, S. Kent. 



Family 3. Coscinoporidae. 

 Sponge-body cup-shaped, stellate, or branched, frequently 

 compressed. Radial canals very numerous, simple, straight 

 blmd. Ostia small ; skeleton finely meshed, dense, strong' 

 prevented from a regular formation of cubical meshes by the 

 numerous radial canals. Crossing nodes of the sexradiates 

 solid, rarely perforated. Covering layer generally deficient 

 or formed by thickening of the outermost skeleton-layer. ' 

 ?Bothrocomcs, King. Permian. 

 Leptopkrayma, Zitt. Cretaceous. 

 Plem'osto7na, Rom. Cretaceous. 

 Guettardia, Mich. Cretaceous, Eocene. 

 Coscmoporaj Goldf. Cretaceous. 



Family 4. Mellitionidae. 

 Sponge-body branched, globular, or lamellar. Wall com- . 

 pletely permeated by numerous tubular water-canals, and* 

 thereby divided into cells like those of a honeycomb. Skele- 

 ton-spicules with solid crossing-nodes. Surface (? naked, or) 

 veiled by a delicate, meshed or porous, siliceous coat, which 

 also covers the apertures of the canals. Root deficient. 

 '^'Ajyhrocallistes, Gray. Cretaceous, Miocene 

 *?Fte?^%m, S. Kent|. 



t The genera marked with an * areliying at the present day. 

 X Also Stauronema, Sollas. 

 Ann. & Mag, N. Hist. Ser. 4. Vol xx. 29 



