011J)ER IV 



SILICISPONGIAE— HEXACTINELLIDA 



65 



composed of large, four-rayed stauractins embedded in a thin, continuous or 

 perforated skin. Very common in Upper Jurassic Spongitenkalk. 



Stauroderma Zitt. Funnel-shaped or plate-like, with broad and shallow 

 cloaca, into which the large, round postica of short canals open. Inner and 

 outer surfaces provided with dermal layer, in which stellate spicules are 

 embedded with reduced externally and internally directed rays. Upper 

 Jurassic. 



Casearia Quenst. Cylindrical, with numerous annular constrictions. 

 Cloaca deep, tubiform ; dermal layer relatively thick, and made up of 

 cemented stellate spicules. Upper Jurassic. C. articulata (Goldfuss). 



Porospongia d'Orb. (Fig. 73). Compressed and expanded, more rarely 

 bulbous or cylindrical. Superior surface pitted with large exhalent apertures 

 of short, blindly terminating cloacae, and covered over with a dense or finely 

 perforate siliceous skin, in which cruciform spicules and regulär hexactins are 



Cypeläa rugosa (Goldfuss). Upper Jurassic ; Streit- 

 berg, Franconia. a, Spoiige, 1/2 natural size ; b, c, 

 Dermal layer, i^/j. 



Porospongia impressa (Goldfuss). Upper Jurassic : 

 Muggendorf, Franconia. a, Fragment in natural size 

 b, Dermal layer, 6/^ ; c, Skeleton, 12/^. 



embedded. Lattice skeleton with cubical meshes ; intersection nodes imper- 

 forate. Upper Jurassic. 



Family 4. Ventriculitidae Toulmin Smith. 



^Fall intricately convoluted ; folds radially disposed, generally vertical in direc- 

 tion. Radial canals ending hlindly. Longitudinal furrows developed along folds of 

 the wall, and either open, or partially covered over with a dermal layer, which is usually 

 formed hy thickening of the outer skeletal layer. Skeletal frameioork with octahedrally 

 perforated nodes. Boots consisting of elongated siliceous fibres united hy transverse 

 hridges and without axial canals. Jurassic and Cretaceous. 



Pachyteichisma Zittel (Fig. 74). Turbinate or bowl-shaped, with very thick, 

 convoluted wall. Folds separated on outer surface by deeply incised furrows, 

 on inner surface by shallow furrows. Framework extremely regulär. Root 

 and dermal layer absent. Upper Jurassic. 



Ventriculites Mantell (Fig. 75). Bowl-, plate-, beaker-, funnel-shaped, or 

 cylindrical, with wide cloaca. Wall thin, convoluted ; folds separated on both 

 sides by closely crowded longitudinal furrows. Lattice-work of skeleton more 

 VOL. I F 



