INVERTEBRATE BOTTOM FAUNA 509 



region, — though, probably owing to the influence of currents, 

 forms Hke Dorocidaris and Waldheimia septata seem to find 

 their most favourable conditions of existence there, and con- 

 sequently are extremely abundant, — but because the plateau- 

 edges are the limits of distribution between the fauna inhabiting 

 the plateaus and the totally distinct fauna of the deep central 

 basin of the Norwegian Sea known as the "cold area." To 

 avoid misunderstanding I may repeat that on the steep slope 

 below the actual edge, and down to a depth of 600 or 800 

 metres, that is to say, to a depth where the temperature does 

 not fall below 0° C, forms belonging to the boreal fauna may 

 be met with. Still these slopes are as a rule so precipitous in 

 comparison with the wide plateaus that, topographically, one 

 is almost entitled to look upon the edges as a boundary region. 

 The bottom of the slopes below the edge itself seems to consist 

 nearly everywhere of soft mud dotted over with large-sized 

 stones, thus providing a home for both mud-bottom forms and 

 hard-bottom forms. 



I have stated that we are still only imperfectly acquainted Fauna of the 

 with the fauna on the bottom of sand and stones upon the p'^*^^"^- 

 plateaus, as only a few systematic investigations have been 

 undertaken here and there. But we know enough to conclude 

 that from a zoo-geographical point of view it is similar to that 

 of the muddy bottom, consisting partly of forms that are common 

 to both the plateaus and the fjords, and partly of forms peculiar 

 to the plateaus which do not enter the fjords. The latter, 

 however, like the corresponding forms of the muddy bottom, 

 are comparatively few. This is confirmed by some dredgings 

 made by the "Michael Sars " in 1906, when researches were 

 carried out on several parts of the Norwegian plateau. 



Without attempting a full description of the lower animal- 

 forms on the plateaus, we may refer to a few of the principal 

 ones. Several hauls by the " Michael Sars " with the trawl in 

 1902 and 1906 showed an abundance of animal life in the 

 northern portion of the North Sea Plateau, on hard sandy 

 bottom (probably mixed with small stones) at depths of 150 

 to 200 metres, belonging to both fjord forms as well as 

 plateau forms : — 



There were numbers of Spatangus (especially vS. rascJii in the greater 

 depths), Echinus acutus forma norvegicns, and Dorocidaris papillata, 

 forms characteristic of the edges, also considerable quantities of Asterias 

 rubens, Porania pulvilhis, Goniaster borealis (?), Echinaster sanguinolentus, 

 Pontaster tenuispinus, Stichaster roseus, Hippasterias phrygiana {plana), 



