198 CALCAEEOUS SPONGES. 



layer of very closely arranged fibres, finer than those of the substance of the wall ; 

 the interspaces between these surface-fibres are hardly visible without a lens. On 

 one surface of this wall, either the upper or under, are minute circular apertures, 

 from '5 to '85 mm. in width and from 1 to 3 diameters apart ; these apertures are 

 connected with sinuous canals, which extend generally at right angles into the wall. 



The fibres of the interior of the wall, measured in a thin section, are from 2 to 

 •4 mm. in thickness ; the filiform spicules are slender, and closely arranged parallel 

 to each other in the direction of the fibre and round the margins of the canals. 



In its mode of growth, and the size of the oscular apertures, this species corre- 

 sponds with Elasmostoma consohrinum, D'Orbig. ; but besides the differences in the 

 spicular structure, which of course can only be ascertained in thin sections, the 

 present species is usually larger and the walls are thicker than in the examples of 

 E. consohrinum from the Cenomanian at Essen. 



Distribution. Lower Green Sand: Farringdon, Berkshire. 



Raphidonema porcatdm, Sharpe, sp. (Plate XXXVII. fig. 3.) 



1854. Manon porcatum, Sharpe, Quart. Jourii. Geol. Soc. vol. x. p. 196, t. 5. f. 2. 



1874. Manon po7-cutum, Davey, Traus. Newbury Field-Club, p. 16. 



1878. Catagma porcatum, Sollas, Ann. & Mag. Nat. Hist. vol. ii. p. 362. 



1883. Catagma porcatum, Keeping, Foss. of Upware &e. p. 147. 



Sponges either cup-shaped or growing in irregularly convolute expansions. Tlie 

 specimens vary from 30 to 70 mm. in height and from 38 to 100 mm. in breadth. 

 The walls are from 4 to 5-5 mm. in thickness. The upper or inner wall-surface has 

 a smooth dermal layer penetrated by numerous, irregularly disposed, circular aper- 

 tures, about "85 mm. in width ; the interspaces between these are minutely porous. 

 The under or outer surface of the wall is covered with sharply projecting sinuous 

 anastomosing ridges ; the fibres of this surface in some examples are finer and closer 

 arranged than those of the interior of the wall, whilst in other specimens there is 

 but little difference between the surface and the interior fibres. 



The interior fibres, as seen in a transverse microscopic section, are from -15 to 

 •3 mm. in width ; the spicular structure resembles that of R. contort um. This species 

 is characterized by the peculiar sinuous ridges of the under surface. 



Sharpe states that the inner surface of this species is pierced by very numerous 

 ill-defined openings, but the oscular apertures only appear ill-defined when the 

 surface is worn ; in perfect specimens they are as clearly marked as in the preceding 

 species. 



Distribution. Lower Green Sand : Farringdon ; Upware. 



Raphidonema pustulatum, Hinde, n. sp. (Plate XXXVI. figs. 8, 8 a.) 

 Sponges either shallow cup- or funnel-shaped, or forming convolute expansions. 



