THE BARENTS SEA 



175 



southwestern part of it (Fig. 73). Derjugin had drawn the boundary between 

 the Arctic and sub-Arctic benthos so far to the east as a result of his obser- 

 vation of the occurrence of some individual boreal forms far to the east. How- 

 ever, this drift of the boreal forms, under continuous pressure of warm waters 





Fig. 73. Zoogeographical boundaries of the Barents Sea. / Boundary be- 

 tween Arctic and Atlantic-boreal sub-regions (Ortmann); // Limit of 

 Arctic region (Broch) : a for plankton, b for benthos ; /// Boundary be- 

 tween Arctic and sub- Arctic regions (Derjugin); IV Boundary between 

 Arctic and boreo- Arctic regions (Hofsten) ; V Boundary between Arctic 

 and transitional Atlantic region (Hentschel) ; VI Boundary between high 

 Arctic and low Arctic sub-regions (Brotzky and Zenkevitch) identical with 

 Schorygin's boundary ; VII Boundary between Arctic and boreal benthos 

 (Filatova), almost the same line as corresponding boundaries of Schorygin, 

 Brotzky and Zenkevitch. 



from the west, has little quantitative effect. The main mass of the fauna remains 

 the same. A sharp numerical change of the fauna from the Arctic to boreal 

 forms takes place much farther to the west. Z. Filatova's (1934) quantitative 

 zoogeographical analysis of the fauna of the southwestern parts of the Barents 

 Sea is very interesting. A count of the ratios of the boreal, Arctic and Arctic- 

 boreal forms of the bottom communities makes it possible to draw a fairly 

 clear boundary between the Arctic and boreal regions. (Fig. 74). This study 



