542 



DEPTHS OF THE OCEAN 



where between 2000 and 3000 metres ; the temperature at the 

 same time falls to about 2-^° C, which prevails everywhere in 



Fig. 386. 

 Oneirophanta sp. "Michael Sars," 1910, Station 10, 4700 metres. 



the abyssal tracts of the Atlantic and other non-arctic waters. 

 The upper limit certainly presents greater difficulties, but I 



^^,. 



4C 



Fig. 387. 

 Freyella sexradiata, Perrier. "Michael Sars," 1910, Station 10, 4700 metres. 



believe that a great many of the forms which characterise the 

 archibenthal belt do not as a rule extend into depths less than 



