M. K. A. Zittel on Fossil Hexactinellida. 505 



the wall reach almost to the centre, and are bounded by two 

 parallel plane walls, which enclose a canaliform space opening 

 into the central cavity. On the blunt edges of the wings 

 there are several large apertures standing one above the other. 

 Both surfaces of the wall are covered with numerous round 

 ostia of fine blind radial canals. Skeleton as in Pleuro- 

 stoma. 



Guettardia stellata, Mich. Ic. Zooph. pi. 30 {excl. fig. 6) . 

 '\Ventricuiites qiiadrangularis^ ]\Iant. Geol. Sup. xv. 6. 



Pleurostoma trilohata, Rom. Spongit. v. 8. 

 ■\ Guettardia Tkiolati, D'Arch. M^m. Soc. G6o\. Fr. 2" 

 s4r. ii. pi. V. 15, pi. viii. 5-7. 



COSCINOPOEA, Goldf. 

 Petr. Germ. i. p. 30. 



Cup-shaped, with ramified roots. Wall covered on both 

 sides with numerous quincunciallj arranged ostia of straight 

 cffical radial canals. Skeleton between the canals formed of 

 very irregular latticework, which becomes thickened by inter- 

 mediate beams both at the surface and in the walls of the 

 canals. Crossing-nodes of the sexradiates in part octahedrally 

 perforated, in part solid. Root consisting of long siliceous 

 fibres united by cross bridges. 



Coscinopora tnfundibidiformis, Goldf. ix. 16, xxx. 10. 

 C. macTopora^ Gold. ibid. ix. 17. 



Family 4. Mellitionidse. 



Apheocallistes, Gray. 



Proc. Zool. Soc. 1858, p. 115. 



Polyzoic, branched, nodose ; the tubular branches closed at 

 the end. Wall consisting of prismatic radial tubes of six-sided 

 form, open at both ends. These perforating radial canals are 

 separated by thin walls of latticed skeleton. The latter con- 

 sists of coalescent sexradiates, which are prevented from taking 

 a regular arrangement by the canals. The crossing-nodes are 

 imperforate. In the recent species a very delicate latticed 

 web covers the surface and the ostia of the canals ; in addi- 

 tion so-called brush-forks are abundantly present as flesh- 

 spicules. 



ScypMa alveolites, Rom. Kr. iii. 6. 

 Aphroccdlistes heatrix, Grray, P. Z. S. 1858, p. 115. 

 A. Bocagei, Wright, Quart. Journ. Micr. Sci. vol. x. p. 4, 

 pi. i. 



