HEXACTINELLIDA 295 



in the ooze, either by a loose tuft of thread-like spicules 

 resembling a wisp of spun glass, as in the Andaman 

 bird's-nest sponge {Pkeronema rapkaims, F. E. Schulze, 

 Fig. 1 8), or by a stiff hollow stem that looks something 

 like a tube of asbestos, as in Saccocalyx pedunculata, F. 

 E. Schulze (Fig. 95), but often they are merely tethered 

 by a long anchor-rope of stout strands of glass tightly 

 twisted together, as in Hyalonema (Fig. 96). 



The Hexactinellida, which are now almost entirely 

 confined to deep water, occur as fossils in almost every 

 geological system from the Cambrian onwards. They 

 are particularly abundant in rocks of Cretaceous age, 

 and the flints of the White Chalk are now generally 

 believed to have originated from Hexactinellid sponges 

 whose skeletons were dissolved, and afterwards re- 

 deposited as nodules round foreign bodies lying at the 

 bottom of the Cretaceous Sea. 



The species obtained by the Investigator are thirty- 

 one in number, of which eight were dredged in depths 

 exceeding 1500 fathoms, and they have been described 

 — the majority being new to science — by Professor F. 

 E. Schulze ; of the few that were already known, two 

 are wide-ranging species that also occur, on the one 

 hand, in the North Atlantic, and, on the other hand, 

 in Japanese seas. 



More than a dozen of them are glass-rope sponges 

 (Hyalonemci) whose anchoring ropes are usually 

 encrusted by zoophytes of the genus Palythoa, and by 



