546 



DEPTHS OF THE OCEAN 



separated areas of the deep sea. And so, too, we could mention 

 deep-water types of particular structure in the case of most of 

 the invertebrate classes. 



Now as these types are distributed over a large portion 

 of the great oceans, and occur there sufficiently generally to 

 give the deep-sea fauna its character, it is fair to assert that 

 this fauna is more uniform than the fauna of the littoral and 

 sub-littoral zones. As is well known, we get great differences 

 in the physical conditions of the different areas of both littoral 

 and sub-littoral zones, consequently we find there greater varia- 

 tions of the fauna than in the deep sea, where physical conditions 

 are uniform, or, in other words, there are more coastal faunal 

 areas than there are deep-sea faunal areas. 



We may briefly characterise the deep-sea fauna as follows : 

 It is largely composed of groups of forms, which morphologically 

 differ in many essentials from the types of the littoral fauna. 

 These groups are distributed over very extensive tracts of the 

 deep sea, but the different species (genera, families) within 

 the groups may be limited to more circumscribed areas. It is 

 evident, therefore, that we can distinguish between the various 

 faunal areas of the deep sea, though we may not yet be able to 

 fix their boundaries.^ 



The second question is how far the deep-sea fauna of the 

 Atlantic resembles that of the Norwegian Sea, or in other 

 words whether the Atlantic area with its higher bottom- 

 temperatures shares many species with the " cold area " of the 

 Norwegian Sea. As indicated on p. 13, Murray in 1886 

 summarised the results obtained in the Faroe Channel by the 

 " Lightning," " Porcupine," " Knight Errant," and " Triton " 

 Expeditions, and showed that of 385 species recorded from the 

 "warm" and "cold" areas, only 48 species (or 12J per cent) 

 were common to both areas. ^' 



The Lycods are especially characteristic of the cold area 

 of the Norwegian Sea, whereas the Macrurids are typical 

 of the deeper parts of the Atlantic, and Jungersen has drawn 

 attention to the abundant horn-corals and joint-corals (Gorgonids 

 and Isids) as well as the "star-corals" {Octilina, Amphihelia) 

 and other corals of the Atlantic deep water, none of which occur 

 in the Norwegian Sea deep basin. 



The finding of such differences in the general character of 



i. 



^ In regard to the boundaries, however, the cold area of the Norwegian Sea forms an ex- 

 ception, and the same may possibly be true of the Antarctic deep sea (Chun, Atts der Tiefe des 

 WelUne.eres ; Mortensen, Echinoidea of the " Tngolf" Expedition). 



'^ See also Murray and Tizard, Proc. Roy. Soc. Edin., vol. xi. p. 638, 1882. 



