DESCRIPTION OF FIGURES ON PLATE III. 

 FLINTS DERIVING THEIR FORMS FROM SPONGES. 



One-Sixth Natural Size. 



These figures are taken, with the exception of the first 

 five (which are from Dixon's Geology of Sussex), from Dr. G. 

 J. Hinde's notable '' Catalogue of the Fossil Sponges in the 

 British Museum." 



1a a fungiform Ventriculite, often termed a fossil mushroom. 



2a Ventriculite, showing foldings of sponge on upper edge. 



3a Ventriculite, with root. 



4a V. Townshendi. 



5a Outline of Ventriculite in Flint. 



6a V. infundibulifor.mis, with transverse section. 



7a Dermal layer of Callodictyon, enlarged a little more than 

 twice. 



8a Structure of Spicules in internal wall of sponge, enlarged 

 as above. 



9a Skeletal mesh of Ventriculite. 



10a Branching Sponge. Up. Greensand. 



11a Empty mould of a branching Sponge in Flint. 



1 Siphonia Tulipa. Up. Greensand, Warminster. 



2 & 3 Vertical and transverse sections. 



4 Siphonia Ficus. Grey Chalk, Dover. 



5 Siphonia Konigi (Choanite). Up. Chalk. 



6 Hallirhoa Costata. Up. Greensand. 



7 „ ,, (One- ninth, natural size). 



8 S. Pyriformis. 



9 Section of same. 



10 Genus Siphonia — Species undetermined. 



11 & 12 Vertical and transverse sections of S. Konigi. 



13 Flint, showing funuel-shaped cloaca of a Sponge, and the 

 courses of the canals opening into it. 



