INVERTEBRATE BOTTOM FAUNA 503 



south, or else are true natives, nowadays at any rate widely dis- 

 tributed throughout the northern seas. Most of the forms met 

 with in the central portion are also to be found along the 

 coasts, but numbers of forms frequenting the coasts, especially 

 shallow-water forms, do not inhabit the plateaus. 



We have not at present sufficient information to describe in 

 detail other plateaus in depths less than 100 metres. The 

 " Michael Sars " occupied two stations in 50 to 100 metres, off 

 south-eastern and south-western Norway, where the fauna did 

 not appear to differ from that in the outer part of the fjords and 

 in the island belt. Certain forms (for instance Balanoglossus, 

 taken off Risor on the south-east coast) have, however, not 

 been taken in the western fjords nor in the central North Sea, 

 but they have been recorded from the west coast of Sweden 

 (Bohuslan). At the localities mentioned we were able to 

 observe the remarkable fact that certain forms (for instance 

 Echinus esculentus, Asterias rudens, Ophiothrix fragilis) occur 

 in comparatively deep water, while in the fjords and island 

 belts they generally occur in the littoral zone only. 



The investigations of C. G. J. Petersen in the Skagerrack 

 show, as far as we can judge from his short statements, a marked 

 similarity to the conditions prevailing in the North Sea. At 

 present it is impossible to enter into a detailed account, and we 

 can only state that along with the similarity there are certain 

 discrepancies : thus, for instance, the pennatulid Pennatula 

 phosphorea has not been captured by the " Michael Sars " in the 

 central North Sea, but it is frequent on the Norwegian North 

 Sea plateau and in the Kattegat. 



2. Continental Plateaus covered by more than iog Metres of 

 Water. — The different lands bounding the Norwegian Sea and 

 North Sea form the emerged portions of larger or smaller 

 submarine plateaus. The bottom on these plateaus varies con- 

 siderably, though, generally speaking, it may be described as a 

 mixture of stones and rock together with fine or coarse sand ; 

 only exceptionally, and in the deeper portions, is it composed of 

 mud. The character of the bottom renders investigations 

 extremely difficult, and the fauna is therefore not so well known 

 as that of the fjords. Where the bottom is covered with 

 softer material the fauna resembles that of the fjords. This 

 is particularly the case in the Norwegian depression or gut, Norwegian 

 running parallel to the Norwegian coast from the latitude of ^^^p^^s^^""- 

 Stat to the Skagerrack. The depth in the middle averages 



