1 6 A Guide to the Zoological Collections in the 



and also in Aphrocallistes and Farrea, all of which are 

 exhibited in the collection. 



In some species the spicules at the base (or root) of the 

 sponge are fused together to form stout threads, which 

 either remain separate or in loosely-woven tufts as in the 

 Bird's Nest Sponge {Pheronema globosum) and in Semper- 

 ella schnitzel^ or are tightly woven together in strands to 

 form a long rope, as in the Glass-rope Sponge {Hyalone- 

 ma). By these tufts or ropes the sponge anchors itself 

 in the mud at the bottom of the ocean. 



The Hexactinellida are represented in the collection by 

 specimens of the following genera : — Euplectella, Au- 

 lochone, Nyalonema, Stylocalyx, Pheronema, Semperella, 

 Aphrocallistes, and Farrea. Some of the forms taken by 

 the spicules of the flinty sponges are shown in the large 

 plate of enlarged drawings in Case 1. 



iii.— PORIFERA CHONDROSPONGI^. 

 [(Ia0c 2]. 



The Chondrospongise, or Horny-Flinty Sponges, form a 

 very large Order of sponges, in which the skeleton is 

 typically made up of a mass of siliceous, or flinty, spicules 

 of various shapes, which are not usually cemented together 

 either by spongin or by flint, but are matted together to 

 form a stout felt-work. 



The Order is fairly well represented in the collection by 

 the following genera : — Tethya, Aulospongus ; Raphyrus, 

 Papillina ; Suberites, Poterion (a series of magnificent 

 specimens of Poterion neptuni), Raspailia, Dictyocylin- 

 drus, Acanthella, Phakelliay Chondrilla, Spongilla. 



iv.— PORIFERA CORNACUSPONGI.^. 



[Case 3]. 



The Cornacuspongise also form a large Order, in 

 which the skeleton is typically made up either of siliceous 



