M. K. A. Zittel on Fossil Hexactinellida. 511 



POROSPONGIA, D'Orb. 



Cours elem. de Paleont. ii. p, 211. 



Lamellarly dilated, more rarely nodular or cylindrical. On 

 the upper surface with more or less numerous circular aper- 

 tures of gastral cavities. The surface provided with oscula is 

 coated with a finely porous or dense siliceous membrane, in 

 which slightly elevated, very large cross-spicules, as well as 

 numerous small sexradiate axial crosses, are imbedded. Under 

 surface veiled by a delicate meshed net of cemented cross- 

 spicules. The wall consists of sexradiates with solid crossing- 

 nodes regularly amalgamated to form cubical meshes of con- 

 siderable size. On the lower surface there are small ostia of 

 very short, slightly developed canals. 



^Afanon marginatum^ Goldf. xxxiv. 9,^, h. 

 *il/. impressum, Miinst., Goldf. xxxiv. 10. 

 *Porospongiafungiformisj Zitt., Goldf. xxxiv. 8, a, 5, c. 



Opheystoma, Zitt. 



Distinguished from the preceding genus by the covering 

 layer, in which there are only small axial crosses, and by the 

 octahedrally perforated crossing-nodes of the skeleton-spicules. 



^Porospongia micrommata^ Kom. Spongit. iv. 14. 

 ? Placochl^nja, Pomel, I. c. 73. 

 Family 7. Maeandrospongidae. 

 Plocoscyphia, Reuss. 



Bohm. Kr. 77. 



Sponge-body nodular, globular, or irregular, consisting of 

 mseandrically twisted, anastomosing or communicating tubes 

 or leaves. Upper surface convex, flat or with a central de- 

 pression. Walls of the tubes very thin, sometimes Avith small 

 ostia. Skeleton consisting of pretty regularly arranged coales- 

 cent sexradiates, with octahedrally perforated crossing-nodes. 

 In some species the lattice-spiculcs near the surface possess 

 imperforate crossing-nodes. 



^Plocoscyphia lahyrinthica^ Reuss, Bohm. Kr. xviii. 10. 

 '^ AcMlleum morchella, Goldf. xxix. 6. 

 ^Plocoscyphia mceandrina^ Horn. Spongit. x. 8. 



TrexMAbolites, Zitt. 



Sponge-body nodular or lamellar, consisting of masandrically 

 twisted, anastomosing, thin-walled tubes or leaves. Upper 



