M. K. A, Zittel on Fossil HexactinelUda. 513 



layers of regularly arranged coalescent sexradiates, with octa- 

 liedrally perforated crossing-nodes. 



Scyphia fungiformisj Goldf. Ixv. 4. 



Ce2)halites campanulatus, Toulmin Smith, l. c. pi. xiv. 

 12, 13. 

 * Camerospongia Schlonbachi, Rom. Spongit. 3, 5. 



Cystispongia, Rom. 



Spongit. 7. 



Pyriform, egg-shaped, completely coated with a dense 

 siliceous membrane, which leaves open only one or a few 

 (2-4) large margined orifices of irregular form ; these orifices 

 are considerably depressed. In the interior there are m^an- 

 drically contorted, very thin-walled, indistinctly radially 

 arranged tubes, the closed ends of which extend into the de- 

 pressions belonging to the large apertures. The lattice- 

 skeleton of the tubes consists of coalescent sexradiates with 

 imperforate crossing-nodes, and usually presents a very irre- 

 gular arrangement, in consequence of arms of sexradiates 

 attaching themselves to tlie crossing-nodes of neighbouring 

 spicules. 



Cgstispongia bursa, Quenst., Rom. Spongit. iv. 7. 



Family 8. Callodictyonidse. 



Callodictyon, Zitt. 



Funnel-shaped, thin- walled. Central space very wide. 

 Wall even, consisting of several layers of coalescent sexra- 

 diates, which form serially arranged quadratic meshes. The 

 crossing-nodes of the sexradiates are octahedrally perforated, 

 the siliceous arms armed with spines. The superficial layer 

 is formed by lamellar dilatation of the siliceous rods of the 

 outer skeletal layers, in which, however, all the meshes remain 

 open for the circulation of water. Canals or ostia are wanting. 



Callodictyon infundihulum, Zitt., n. sp. (Upper Cretaceous 

 of Ahlten.) 



Marshallia, Zitt. 



Like the preceding genus, but the thin wall furnished with 

 a few broad, spiral or longitudinal folds, upon the back of 

 which there are some isolated large apertures. 



*Pleurostoma tortuosum, Rom. Spongit. vi. 1. 

 * Coelopfi/chium alternans, Rom. Kr. iv. 6. 

 Ann. (Sc Mag. N. /list, Ser. 4. Vol. xx. 35 



