502 DEPTHS OF THE OCEAN 



instance, the case with the crab Corystes cassivelanus (see Fig. 

 353), the mussel Mactra stultorum, the shelled snail Natica 

 catena, and the tube-worm Sabellaria alveolata, all of which were 

 found west of Jutland to the north of lat. 56' N. The last 

 mentioned was met with at only one station (depth 41 metres, 

 temperature 8.7" C), but in large quantities and big colonies; 

 while the other three were taken in shallow water (less than 

 40 metres) with the highest temperatures observed during the 

 cruise (10° to 12^ C). The characteristic ribbon-like egg-clusters 

 of Natica were found as far out as the northern slopes of the 

 Dogger Bank, where the animal itself had been previously 

 captured. According to Professor Plate both Natica catena and 

 Mactra stultorum occur on the Great Fisher Bank, which shows 

 that these forms do sometimes leave the coast region. On the 

 other hand, Corystes seems exclusively to follow the coasts of 

 Britain and Denmark, since we did not capture it with our 

 trawl on the Dogger Bank, though depths and temperatures 

 appeared to be favourable, and it has not been recorded at any 

 great distance from the coast. These forms are found along 

 the shores of Britain, and penetrate into the northern part of 

 the Kattegat, but, if we except Mactra stultoru7n, they do not 

 reach the coast of southern Norway. 



Our knowledge regarding the faunal character of the North 

 Sea may be briefly recapitulated as follows : In the southern- 

 most portion, at depths down to 40 or 50 metres, where the 

 water-layers in summer attain a temperature of 13°-! 5' C, but 

 in winter are cooled down to 4 or 5 C, the fauna consists 

 partly of northern elements capable of adapting themselves to 

 variations of temperature, and partly of a special southern 

 contingent that has wandered in through the English Channel 

 and requires high temperatures for at any rate part of the year. 

 Most of these latter forms are limited to the southernmost 

 portion, though a few follow the coasts towards the north, 

 penetrating on the east side even to the Skagerrack, and on the 

 west side to the coasts of Northumberland or perhaps still 

 farther, but avoiding the deeper parts of the central area. The 

 northernmost portion of the plateau, where the depths exceed 

 100 metres, but where, notwithstanding, the waters are warmer 

 than in the central parts, is characterised in similar fashion, as 

 we shall presently show, partly by special southern deep-water 

 forms that have wandered in past Shetland and only very rarely 

 get as far as the coast of Norway or the Skagerrack, and partly 

 by forms which may either have arrived originally from the 



