HYDROIDA II 



181 



quently met with in Davis Strait, which is thus proved to belong, at any rate in part, to the boundary 

 waters of the boreal region. Yet the species penetrate only quite exceptionally into the west Green- 

 land fjord area, which must be regarded as purely arctic, partly on account of the intermixture of 

 melting water from the glaciers, and partly owing to the north-going branch of the East Greenland 

 Polar Current, which turns round Cape Farewell and runs some distance up the coast Here we still 

 find Dynamena pumila sporadically, probably because the investigations were carried out at a time 

 when the summer heat had brought the surface temperature up a little, enabling the species just to 

 exist for a brief wb'' M and under difficulties. Not until we reach the waters between Holstensborg 



loo m. 



. boom 



._._ ._._._ looom. looom. 



Fig. XCI. The occurrence of Halecium muricatum, and Sertularclla tricuspidata, two arctic species which 

 penetrate into the southern parts of the boreal region. (The red line approximately indicates the limit 



of the cold area). 



and Egedesminde do the boreal elements in the coast fauna become more pronounced. In Danmark 

 Strait, between Greenland and Iceland, we see that the finds group themselves closer as soon as we 

 pass south of the o isotherm, where the depth conditions are more favourable. Despite their positive 

 bottom temperature, the shallower North-Icelandic waters seem to take a more arctic character, though 

 this may, as we shall presently see, perhaps be equally well explained as due to insufficient investi- 

 gation. Between Iceland and the Faroe Islands, the species move up to the verge of the cold area, 

 but do not pass it And the whole of that part of the Norwegian coastal banks which falls within 

 the limits of the chart presents an entirely boreal character. 



Turning now to the other side, and taking the distribution of the arctic-boreal species Hale- 

 cium muricatum and Sertularella tricuspidata, several peculiarities are also here apparent (fig. XCI) 



