288 Ih. Mortensen. 



Grieg, Öslergren, Michail ovskij , Kali schewskij and the 

 present author, on the northern Echinoderms, the knowledge of the 

 fauna and its distribution, and of the oceanography and hydrography 

 of the northern Seas has been so very considerably extended that 

 it now seems possible to clear up the zoogeographical relations of 

 this fauna, at least in its main features. 



It may prove useful as an introduction to this study to give a 

 short summary of the hydrography of the Greenland Seas. 



The great depths of the Atlantic continue northwards on each 

 side of Greenland to about Lat.66°N. Here a submarine ridge forms 

 the boundary between the Atlantic Deep-Sea and the Northern or 

 Polar Deep-Sea. The ridge running across the Danmark Strait from 

 Northwest Iceland in a northwestern direction to East Greenland 

 separates the warm bottom water of the Atlantic from the ice-cold 

 bottom w^ater of the Polar basin. In the Davis Strait the ridge 

 running from Holstensborg to Cape Walsingham on Baffin Land 

 separates the great depths of the Davis Strait from the deep basin 

 of Baffin Bay, thus stopping the passage northwards of the warm 

 bottom water of the Atlantic Deep-Sea. The deep basin of the Baffin 

 Bay is, on the other hand, limited to the North by the shallow 

 water of Smith Sound. The Sea to the North of Greenland is still 

 loo little explored, but it seems j3robable that the great depths of 

 the Sea North of Iceland are in direct continuation with the depths 

 of the Polar Sea. 



While thus the deep sea of Greenland is divided into two very 

 distinct regions, a 'warm and a cold area, the conditions of the lit- 

 toral regions are more complicated. Along the East Coast the great 

 Polar Stream passes downwards, round Cape Farvel and then north- 

 wards along the West Coast, bringing with it the great ice masses 

 and the cold polar water. Along the West side of the Davis Strait 

 the cold Labrador Stream passes southwards, bringing the arctic 

 conditions far dow4i along the American coast and making its influ- 

 ence felt as far South as Cape Cod (about Lat. 42°N.). In the Dan- 

 mark Strait the warm Atlantic water flows northwards along the 

 West Coast of Iceland (the Irminger Stream); at the ridge it passes 

 across the Danmark Strait towards the Greenland Coast and then 

 passes southwards. The polar water, being less saline than the At- 

 lantic water, occupies the upper layers of the sea, down to ca. 

 200 m. Its temperature is about 0°, while the Atlantic water has a 

 temperature of 3° even down to 2000 m. At this part of the coast 

 of East Greenland, from about Angmagsalik, and likewise along the 

 West coast at least until the Holstensborg ridge, the influence of 

 both a cold and a warm-water stream may thus be expected to be 



