450 



THE VOYAGE OF H.M.S. CHALLENGER. 



in this respect. It is very probable, however, that the tropical zone of the Indian Ocean, 

 which has not hitherto been investigated, will prove to be richer in species than that of 

 the Pacific, since in its south temperate zone, which at present is alone available for 

 comparison, it has shown itself to be richer. Hence we may anticipate that an investi- 

 gation of the tropica] region of the Indian Ocean would yield specially rich material as 

 regards the Hexactinellida. 



" Finally I will give the principal results of an inquiry undertaken to find out the 

 dependence of the Hexactinellida upon the nature of the sea-bottom. For this purpose 

 the Stations were classed according to the nature of the deposit found at each. 



" When the different groups of Stations were examined it appeared that the Diatom 

 ooze was specially favourable to the Hexactinellida, and also that Radiolarian ooze and 

 blue mud were more or less adapted to their existence ; while they apjaeared to be entirely 

 wanting upon bottoms of sand and gravel, which is perhaps owing to the fact that deposits 

 of this kind usually occur at depths of less than 100 fathoms, which are too shallow for 

 these animals. 



"It is also worthy of remark that several Hexactinellida, which came from great 

 depths, were filled with Diatoms and Radiolarians, although the bottom at these Stations 

 was not a Diatom or Radiolarian ooze." 



The following is a list of the genera contained in the above mentioned families and 

 subfamilies. 



Type CCELENTERATA. 



Subtype Spongiee. 



Class Siucispoxgi^. Subclass Hexactinellida. 



Order I. LYSSACINA, Zittel. 



Family I. Eupi.ectellidvE. 



Subfamily 1. Euplectellinaj. 



(1) Eupkddla, Owen. 



(2) Reyadrella, Osc. Schmidt. 



Subfamily 2. Holascinae. 



(1) Holascus, n. 



(2) Malacosaccus, n. 



Subfamily 3. Tajgeriiwe. 



(1) Ttegeria, n. 



(2) Walteria, n. 



(3) Habrodidyum, Wyv. Thorns. 



(4) Eudictyum, Marshall. 



(5) Didyocalyx, n. 



(6) Rhabdodidyum, Osc. Schmidt. 



(7) Rlwbdopedella, Osc. Schmidt. 



(8) Hertu-iijia, Osc. Schmidt. 



Family II. Asconematid,*. 



Subfamily 1. Asconeniatin;e. 



(1) Asconema, Sav. Kent. 



(2) Aulascus, n. 



Subfamily 2. Sympagellinte. 



(1) Sympagelld, Osc. Schmidt. 



Subfamily 3. Caulophacina\ 



(1) Cunhqihunif, n. 



(2) Trachycaulus, n. 



Family III. Hyalonematid^;. 

 Subfamily I. Hyalonematina'. 



(1) Hyalonema, Gray. 



(2) Didyosphara, n. 



(3) Pherorwma, Leidy. 



(4) Poliopogon, Wyv. Thoins. 



Subfamily 2. Semperellinn'. 

 (1) Semperdla, Gray. 



