M. K. A. Zittel on Fossil Hexactinellida. 419 



Family 7. Mgeandrospon^dse. 



Sponge-body consisting of majandrically tortuous and anas- 

 tomosing thin-walled tubes or laminae. Canal-system defi- 

 cient or scarcely developed. Intercanal-system always present. 

 Covering layer deficient or forming a connected siliceous coat 

 upon the surface. 



a. Without special covering layer. 



PlocoscypMa^ Reuss. Cretaceous. 



^Bactylocalyx^ Stutchb. 



'^ Periphragellciy Marsh. 



'^Myliusia^ Gray (p.p.). 



h. With a covering layer. 



Tremabolites^ Zitt. Cretaceous 

 Etheridgia^ Tate. Cretaceous. 

 Toulminia, Zitt. Cretaceous. 

 Camerospongia, D'Orb. Cretaceous. 

 Cystispongia^ Rom. Cretaceous. 



Family 8. Callodictyonidse. 



Sponge-body cup-shaped. Wall consisting of very regular, 

 wide-meshed latticed framework with octahedral crossing- 

 nodes ; canal-system wanting or confined to the covering 

 layer of the outer surface, which is sometimes very thick. In 

 the interior of the wall the circulation of water takes place 

 directly through the meshes of the latticed skeleton. 



a. Wall naked. 

 Callodictyon, 7a\X. Cretaceous. 

 Marshallia, Zitt. Cretaceous. 

 Becksta, Schluter. Cretaceous. 



b. Outer surface of the wall furnished with a thick covering 



layer, which agrees in structure with the tissue of the 



root. 

 Pleurope, Zitt. Cretaceous. 

 Diplodictyon, Zitt. Cretaceous. 



Family 9. Coeloptychidae. 



Sponge-body umbrella-shaped, stalked. Wall thin, deeply 

 folded, the central cavity divided into radial chambers. Upper 

 surface flat or depressed, entirely coated with a connected 

 covering layer, which generally consists of attenuate finely 

 and coarsely porous bands. Canal-ostia only upon the lower 

 surface of the umbrella upon the back of the folds, sometimes 

 also on the stalk. Latticed framework with large regular 

 cubical meshes. The crossing-nodes of the coalescent sex- 



29* 



