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



a. Canal-system well-developed. Ostia of the ceecal radial 



canals alternate on the two surfaces. 

 '^Prolospongia^ Salt. Silurian. 



Calathium^ Billings. Silurian. 



Archceocyathus, Billings. Silurian. 

 '^Tracliyum^ Billings. Silurian. 

 1 Steganodictyon^ M'Coy. Devonian. 



Tremadictyon, Zitt. Upper Jura. 



Craticularia^ Zitt. Middle and Upper Jura, Cretaceous, 

 Miocene. 

 ?Euhi'ockus, Sollas. Gault. 



Spkenaulax, Zitt. Upper Jura. 



Sporadojjyle, Zitt. Upper Jura. 

 ''•' Sclerothamnus, Marsh, f 



b. Canal-system wanting or scarcely developed. 

 ^Farrea, Bow, Tertiary. 



*Eu7'efe, Marsh. 



Verrucocoelia. Upper Jura, Cretaceous. 

 ^Aulodicfyon, S. Kent. 



Family 3. Coscinoporidae. 



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

 compressed. Radial canals very numerous, simple, straight, 

 blind. 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. 



?Bothroconus, King. Permian. 

 Leptophrayma, Zitt. Cretaceous. 

 Pleurostomaj Rom. Cretaceous. 

 Guettardia^ Mich. Cretaceous, Eocene, 

 Coscinopora^ Goldf. Cretaceous. 



Family 4. Mellition^dae. 



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. 



'^ Aphrocallistes, Gray. Cretaceous, Miocene. 

 *? Fieldinyla, S. Kent \. 



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

 X ALso Stauronema, Sollas. 

 Ann. & Mag. N. Hist. Scr. 4. Vol. xx. 29 



