484 



THE DEPTHS OF THE SEA. 



[chap. 



such recent forms as Aphrocallistes, Iphiteon, Sol- 

 tenia, and Askonema 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 Aphrocallistes Beatrix, 

 we have no difficulty in working out its structure, 

 even to the most minute microscopic detail. 



Other sponges, belonging chiefly to the Lithistidie 



and the Corticatoe, 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 Esperiadae, 

 send out lon^ delicate 

 tubes, which contract 

 slightly, but in 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 

 Choanites. 



One sponge belonging to the group is represented 

 at Eig. 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 



Fig. 81. — Ventriculites simplex, Todlmin Smith. 

 Outer surface ; four times the natural size. 



