M. K. A. Zittel on Fossil Hexactinellida. 507 



Ventriculites, Mantell. 



Fossils of the South Downs, pp. 167-178. 



Sponge-bod J basin-shaped, cup-shaped, cylindrical or funnel- 

 shaped. Central cavity wide. Wall mseandrically folded, the 

 folds either on one or on both sides separated by longitudinal 

 furrows, or pressed close together. Radial canals numerous, 

 rather wide, generally standing in longitudinal rows, always 

 c£ecal ; their ostia arranged in very various ways, sometimes 

 present on both sides, sometimes replaced on the inner or 

 outer surface of the wall by furrows. Skeleton consisting of 

 coalescent sexradiates with octahedral crossing-nodes : their 

 arrangement more or less irregular ; meshes rather large. 

 The surface of the wall and of the canals thickened into a 

 porous covering layer by lamellar dilatation or thickening of 

 the beams of the sexradiates. Root formed of long longitu- 

 dinal fibres without axial canals, united by cross bridges. 



Ventriculites 'striatits, Toulmin Smith, Ann. &Mag. N. H. 

 1848, vol. xiii. 6, 13. 

 ^ScT/phia (Eynhauseni, Goldf. Ixv. 7. 

 '^ Coeloptychium muricatum, Rom. Kr. iv. 16. 



Scyphia angustata, Rom. Kr. viii. 10. 

 *>S'. Zippeiy Reuss, Bohm. Kr. xviii. 5. 



SCHIZOEHABDUS, Zitt. 



Rod-like, slightly enlarged upwards. The whole wall slit 

 on one side from the margin to the commencement of the root. 

 Both sides furnished with repeatedly divided longitudinal 

 furrows, in which are the ostia of the csecal radial canals. 

 Root very much elongated, simple, i-arely with lateral buds ; 

 furrowed on the surface, with numerous vertical tubes in the 

 interior. JMicrostructure as in Ventriculites. 



Schizorhabdus libycus, Zitt., n. sp. 



Tretostamnia, Pomel. 

 Paleontologie de I'Oran, p. 70. 



Rhizopoterion, Zitt 



Sponge-body cup-shaped, passing gradually below into a 

 very thick, elongated stalk, which emits side branches at its 

 base. Both surfaces of the upper cup-shaped part covered 

 with elongated oval ostia of caical radial canals standing in 

 alternating longitudinal rows. The radial canals acquire a 

 more and more obli({ue direction downwards, and finally be- 

 come converted into vertical tubes, which, in great numbers, 



