72 SILICEOUS SPONGES. 



Jekea excavata ■?, Michelin. 



Jerea excavata, Michelin, Icon. Zooph. p. 135, t. 39. f. 2. 

 Jerea excavata, Zittel, Studien, II Ab. p. 81, t. 10. f. 1. 

 Rhysospongia pictonica, Court. Ep. foss. t. 1. f. 1, 2. 



Sponge massive, hemispherical, the upper surface slightly concave, the under 

 surface rounded, apparently sessile. Height 70 mm., width 138 mm. 



Numerous canal-apertures, 3'5 mm. in width, open into the shallow depression of 

 the summit and also on the sides. The only specimen is a solid mass of flint which 

 merely retains the outer form and the canal-apertures. In the absence of the spicular 

 structure, it can only be doubtfully referred to Michelin's species. 



Distribution. Upper Chalk : Wiltshire. 



Genus NELUMBIA, Pomel, 1872. 



Nelumbia tubekosa, Hinde, n. sp. (Plate XVI. figs. I, 1 a, 1 b, 1 c.) 



Sponge club-shaped, with an irregularly truncated summit, gradually tapering at 

 the basal end to form root-like processes. A few irregularly scattered nodose 

 projections are present on the surface. Length 180 mm., width 34 mm. 



Numerous circular or polygonal canals, 3 mm. wide, open at the summit, and 

 extend vertically nearly to the base of the sponge. Another series of canals, 1 mm. 

 wide, extend from the lateral surfaces, in a slightly arched direction, to the central 

 portion of the sponge. 



The spicules of the interior mesh, though now replaced by calcite, can be fairly 

 recognized. They appear to possess smooth robust arms, "27 mm. in length by 

 •045 mm. in width, and prominent junction-nodes. The surface appears to have 

 been completely covered with a delicate dermal layer principally composed of the 

 horizontally extended heads of trifid spicules with bifurcate, straight, pointed rays. 

 Some of the spicular heads are "6 mm. in width. 



In the size and form of the specimen itself, and of the canals, this species difi'ers 

 from the different forms figured by Courtiller* under the name of Polystoma, which 

 have been placed by Pomel as the types of the genus Nehtmbia. In Pomel'sf 

 definition it is stated that the vertical canals do not penetrate deeply below the 

 summit of the sponge ; but, as already indicated by Zittel, it seems very probable 

 that he is mistaken on this point, for in the figures of the type species the canals are 

 shown, in the section of at least one specimen, to extend to the basal portion of 

 the sponge. 



Distributioou Grey Chalk: near Dover. Upper Chalk : South of England. 



* Eponges fossiles, p. 10, t. 15. 

 t Paleontologie d'Oran, p. 194. 



