PLATE XXXVII. 



Page 

 Fig. 1. Elasmostoma plicatumjHinde. Natural size. Showing the upper or inner surface 



of the wall with the oscular apertures. From the Craie Chloritee at Cap la 



Heve, near Havre 196 



Fig. 2. Raphidonema contortum, Hinde. Natural size. A specimen with convolute walls, 

 showing minute oscular apertures on the lower or outer surface of the wall and 

 a smooth dermal layer on the upper surface. From the Lower Green Sand at 

 FarringdoUj Berkshire 197 



Fig. 2 a. The same. A portion of the outer oscular surface of the wall of the same speci- 

 men as fig. 2, enlarged eight times, showing the circular oscular apertures and 

 the minute irregular perforations of the interspaces. 



Fig. 2 b. The same. A portion of the interior fibre, enlarged seventy-two times, showing 

 the filiform three-rayed spicules. Drawn from a transparent section. 



Fig. 3. Raphidonema porcatum, Sharpe, sp. Natural size. An irregularly convolute speci- 

 men, showing the sinuous anastomosing ridges of the under or outer surface of 

 the wall. From the Lower Green Sand at Farringdon 198 



Fig. 4. Raphidonema macropora, Sharpe, sp. Natural size. A small cup-shaped example, 

 showing the nodose outer surface of the wall and a portion of tlie interior 

 surface with the horizontally disposed apertures in the dermal layer. From the 

 Lower Green Sand at Farringdon 199 



Fig. ij. Raphidonema Farringdonense, Sharpe, sp. Natural size. An average specimen, 

 showing the nodose character of the outer surface of the wall and a portion of 

 the interior, with the irregularly disposed canal-apertures. The smooth dermal 

 layer of the interior is limited in this specimen to the lower portion of the 

 surface of the cup. The smooth surface which conceals the canals near the 

 upper margin to the right is produced by an adnate polyzoon. From the 

 Lower Green Sand at Farringdon 200 



Figs. 5 a, b. The same. Fragments of the fibres of the interior, enlarged seventy-two times, 

 showing the closely arranged filiform three-rayed spicules. The fibres are 

 surrounded by a layer of crystalline calcite. Drawn from a transparent micro- 

 scopic section. 



Fig. 6. Fharetrospongia Strahani, Sollas. Natural size. A cup-shaped example, showing 

 the thickness of the wall and the smooth reticulate character of its inner surface. 

 From the Upper Chalk of Kent 201 



