INVERTEBRATE BOTTOM FAUNA 511 



not find there many of the forms that on the west coast of 

 Norway are chiefly distributed in the great depths of the fjord ; ^ 

 there are also certain forms living in deep water at the Shetlands 

 having a southern distribution, Atlantic or Mediterranean 

 forms which find their northern limit there. These differences 

 may to some extent be due to the warm Atlantic water which 

 flows over the Shetland plateau ; thus the " Michael Sars " 

 found a temperature of 9, 12° C. on the western edge at a depth 

 of 300 metres, and captured with a line a southern shark 

 (Hexanchus griseus), frequently taken by British fishermen, 

 which has never been caught farther north in the Norwegian 

 Sea, It is interesting to remark that some of the forms, though 

 no doubt only stray individuals, make their way eastwards along 

 the northern portion of the North Sea plateau as far as the 

 edge of the Norwegian depression, beyond which, however, 

 they never pass, like the crab Portunus tuberculatus ' and the 

 starfish L7iidia ciliaHs, which were captured on the northern 

 slope of the Viking Bank. Others penetrate even into the 

 Norwegian fjords, like the hermit crab Pagurus meticidosus 

 {tricarinatus), and the crab Atelecyclus septemdentatus, small 

 individuals of which were captured on several occasions in the 

 Bergen fjord. Some of the southern forms occurring off the 

 Shetlands wander down along the east coast of Scotland and 

 England, though without spreading farther eastwards, and we 

 find the same faunal agreements and dissimilarities between 

 the east coast of Britain and the west coast of Norway as in 

 the case of the Shetlands. 



Certain parts of the plateaus, at a depth of 100 to 1 50 metres, 

 seem to be favourite abodes of the hydroids, which form regular 

 forests on the bottom, and are plentifully represented by both 

 species and individuals. Just as with the hydroid fauna in the 

 laminaria tracts, so here, too, an assemblage of other animal 

 groups, especially lower crustaceans and naked molluscs, live 

 upon and among these hydroids.^ 



The hydroids appear to occupy comparatively large tracts 

 of the plateaus, though not regularly distributed over their 



^ For instance, Stichopus treinitlus, Bathyplotes tizardi, Amphiura norvegica, Pandalus 

 propinquns, Mimida temdniana. 



^ A specimen of this species was also taken on the deeper part of the slope, in 275 metres, 

 with a temperature of 7-94° C. 



^ Characteristic and common forms of hydroids were : Thujaria thuja, easily recognisable 

 owing to its verticillate branches, Hydrallmannia falcata, Diphasia abietina and D. fallax, 

 Sertularellatrkuspidata, Lafoea s])., Canipmiidana volubilis. Among the lower crustaceans it 

 is especially the caprellids {.-Eginella spinosa) and the arcturids {Astacilla longicornis and 

 Ardiirus sp.) which climb about among the hydroids by means of their specially adapted feet. 

 /Eolids too creep about here in great numbers. 



