INVERTEBRATE BOTTOM FAUNA 531 



where in both the arctic and the boreal regions, while others are 

 generally limited within the arctic region to water having 

 temperatures just about or above o' C. These last are inter- 

 mediate forms between this and the following category, and 

 include, for instance, the prawn Pandalus borealis. 



A third category of species composing the arctic fauna con- Boreal forms 

 sists of boreal forms that are able to enter the arctic region a^-cJlc'^"'^" 

 owing to the warmth introduced by various branches of the distribution. 

 Gulf Stream, which counteracts the chilling effects of the icy 

 coastal and polar currents. On the coasts of East Finmark 

 and on the Murman coast these are particularly in evidence. 

 These boreo-arctic intermediate areas occupy that portion of 

 the Norwegian Sea where the waters of the Gulf Stream and 

 polar currents intermingle, or where the shallow coast waters 



(r^^ 



FUJ. 373. 

 Hippolyte polaris, '^ah. Reduced. (After Parry. ) 



acquire a high summer temperature in consequence of the 

 comparatively milder climate produced by the proximity of the 

 Gulf Stream. 



This boreo-arctic area contains certain forms of truly arctic 

 origin, less sensitive in regard to temperatures above o'' C, and 

 attaining here the extreme limits of their advance in a boreal 

 direction. It also contains genuine boreal species, which may 

 range as far south as the Mediterranean, and have their 

 northern limit within this area. 



,. Along the north-west coast of Norway from Lofoten to the Boreo-arctic 

 North Cape (West Finmark) the character of the fauna is very ^''^^^• 

 complicated, owing to the diversified hydrographical conditions, 

 especially in the deeper places of the coastal area compared 

 with those in the inner basins of the fjords. Many of these 

 north-western fjords are open to the ocean for part of their 

 length, so that their seaward portions may fairly be regarded 



