484 THE DEPTHS OF THE SEA. [chap. x. 



such recent forms as AphrocaUistes, IphUeon, Sol- 

 tenia, and Aslwnema with certain series of the chalk 

 Ventriculites, there cannot be the slightest doubt that 

 they belong to the same family-in some cases to 

 very nearly allied genera. Pig. 80 represents a very 

 beautiful specimen of Ventriculites simplex preserved 

 in flint, for which I am indebted to Mr. Sanderson of 

 Edinburgh. Looking at this in the light of our 

 knowledge of Euplectella or AphrocaUistes beatrix, 

 we have no diflaculty in working out its structure, 

 even to the most minute microscopic detail. 



Other sponges, belonging chiefly to the Lithistidse 



and the Corticatse, re- 

 produce with wonderful 

 accuracy the more irre- 

 gular sponge-forms of 

 the chalk and green- 

 sand ; and a group, as 

 yet undescribed, but 

 apparently an aberrant 

 family of the Esperiadse, 

 send out long delicate 



PiO il.—Ventrmdltes simplex, ToutmiN Smith. tUUCS, WlllCn COntraCt 

 Outer surface; four times the naturaUi.0. ^^{^^^1^ , but iu a mOSt 



characteristic way, at the point of their insertion 

 into the sponge body, recalling very forcibly the 

 peculiar manner in which the tube-like root processes 

 join the sponge in such genera as the vaguely defined 

 Ghoanites. 



One sponge belonging to the group is represented 

 at Pig. 83. A sphere 15 to 20 mm. in diameter con- 

 sists of a smooth glossy external rind, composed of 

 closely meshed pin-headed spicules, with two kinds 



