Plate 18. 



rig. 1. Gellius perforatus. Upper surf ace ; from a photograph ; }. 

 " 2. Oceanapia liaciUifera. Fistula; from a photograph ; |. 

 " 3. Hymeraphla, sp. incriisting Oceanapia bacUlifera. Spicules ; x 450. 

 " 4. Oceanapia bacillifera. Tangential section through wall of fistula, showing 



arrangement of skeletal spicules and spoiigin. Meshes 

 in the skeletal framework, which in the figure are 

 represented as vacant, are filled with parenchyma; x 70. 

 " 5. Tylodesma alba: Megascleres ; x 70. 



6. " " Sigmata ; x 450. 



" 7. " " From a photograph. Sponge viewed obliquely from the side, 



so that upper surface is seen ; \. 

 " 8. Tylodesma iH'stibuhiris. Megascleres ; x 70. 



9. " " Sigmata ; x 450. 



" 10. PhakelUa lamelliijeni. Outer surface of skeletal framework. Piece has been 



macerated in potash. From a photograph; x 5. 



