SIPHOXIA. 65 



The spicules of the stem are elongated and thread-like. No dermal layer has been 

 preserved. 



This species is extremely abundant in the Upper Green Sand of Blackdown and 

 Warminster. The Blackdown examples usually have a sharp constriction between 

 the basal portion of the body of the sponge and the stem, which also is of a slender 

 character. The Warminster examples, on the other hand, have more elongated 

 bodies, which not infrequently gradually taper below to form a stem of considerable 

 robustness. There are, however, both at Blackdown and Warminster, specimens 

 exhibiting characters intermediate between the two extremes, so that it is quite 

 impracticable to limit this species merely to forms which possess the marked con- 

 striction between the body and the stem. In all other features the specimens from 

 these two localities appear to be similar. 



Distribution. Upper Green Sand : Blackdown, Warminster. 



SiPHOnA LN'CRASSATA, GoIdfuSS. 



1833. Siphonia incrassata, Goldfass, Petref. Th. 1, p. 17, t. 30. f. 3. 

 1878. Siphonia incrassata, Zittel, Stadiea, II Ab. p. 79. 



Distribution. Planer-Kalk : Bohemia. Craie Chloritee: Vaches Noires ; Sud- 

 merberg. 



SiPHOXiA ncrs, Goldfuss. (Plate XIII. figs. 3, 3 a.) 



1833. Siphonia ficus, Goldfuss, Petref. Th. 1, p. 221, t. 65. f. 14. 

 1878. Siphonia ficus, Zittel, Studien, II Ab. p. 79, t. 9. f. 6. 



Sponges fig-shaped or subspherical, with gently rounded summits, either apparently 

 sessile or with short branching stems. An average specimen is 75 mm. in height 

 and the same in width. The cloaca is cup- or funnel-shaped; it extends to nearly 

 the centre of the sponge ; the margins are sharp. In an average specimen it is 

 23 mm. in width at the summit. The interior surface exhibits the closely disposed 

 apertures (2"25 mm. each in width) of the canals which open into it. Branching 

 canals also radiate from the cloacal aperture over the surface. The spicular mesh is 

 entirely replaced by calcite, and the forms of the individual spicides are nearly 

 entirely obliterated. The outer surface of the specimens is now smooth and only 

 exhibits- a delicate fibrous network. 



Distribution. Grey Chalk : near Dover. 



SiPHoyu KoxiGi, Mantell, sp. (Plate XIII. figs. 4, 4 a.) 



1822. Choanites Konigii, Mantell, Geol. of Sussex, p. 179, t. 16. f. 19, 20. 



1808. A Flint, from a gravel-pit, Parkinson, Organic Eemains, vol. ii. p. 100, t. 9. f. 1. 



1850. Choanites Konigi, Dixon, Foss. Sussex, t. 17. f. 1, 3, 4. 



1854. Choanites Konigi, Mantell, Medals of Creation, p. 234, f. 1, 3, 4. 



