GENERAL INTRODUCTION TO THE ZOOLOGICAL REPORTS. 



35 



there can be no doubt that at depths which may be regarded as of comparatively easy 

 access, say a little above 2000 fathoms, the fauna is sufficiently varied. The tal)le on pages 

 36 and 37, taken from the " Station-book " 

 gives the number of occurrences of repre- 

 sentatives of the principal gToups of marine 

 animals at the fifty-two stations at which we 

 dredged or trawled successfully at depths 

 greater than 2000 fathoms during the voyage. 

 All the groups marked with a cross were re- 

 presented, having been observed and noted 

 when the trawl or dredge came up ; it is very 

 prolmble that when the detailed lists are com- 

 pleted we shall find that many, particular!)' 

 of the smaller forms, have been omitted. The 

 occurrence of fishes, of cephalopods, and of de- 

 capod crustaceans must be taken with a reserva- 

 tion, as it was not always possible to determine 

 whether they were taken on the bottom, or 

 above it during the hauling in of the net. 



The abyssal fauna would seem, however, 

 to attain its fullest development in a zone of 

 depth between 600, and 1000 or 1200 fathoms ; 

 between these depths where the nature of the 

 material of the bottom is suitable, there is the 

 greatest abundance of Hexactinellid Sponges, 

 of the characterestic deep-sea Alcyonarians, 

 of Stalked Crinoids and Sea-urchins allied to 

 Asthenosoma and Salenia, of the Elpididaa 

 among the Holothuroidea, and of other special 

 types. From 1200 or 1500 fathoms down- 

 wards, the fauna, although becoming aj^par- 

 ently more scanty, maintains much the same 

 character ; and it seems to bear to the richer 

 band at its upper limit somewhat the same 

 relation as to derivation and mixing, which the 

 fauna of the infra-niedian zone of Forbes at 

 60 to 100 fathoms bears to the median zone. 



It would appear that round all coasts, except, perhaps, those within or ])ordering upon 

 the Arctic and Antarctic regions, at a depth of from 100 to 200 fathoms the extension 



9 



Ui/alonema sicboUi, Gray. A Hexactinellid Sponge 

 (much reduced). 



