292 



Depth in 



fms. 



3. XI. 



6. XI. 



8. XI. 



10. XI. 



24. IV. 



8. V. 



9. V, 



0. 





. 0°0 



—2° 2 



—2° 4 



—2° 4 



-0°8 



-1°3 



0°0 



5. 







. -1°2 



— 1°0 



-1°5 









10. 





. 1°3 



— 0°9 



— 0°7 



— 0°9 . 





—0° 2 



0°0 



20. 





. 1°9 



— 0°4 



— 0°7 



—0° 6 . 





— 0°2 





25. 











— 0°3 









30. 







. -0°3 



-0° 3 



0°4 . 





0°3 





40. 





. 2° . . . 





1°0 



1°0 



. 0°0 



0°5 





42. 









50. 















60. 







. -0°0 











70. 









. 0° 3 



0°4. 





1°6 





80. 





. 0°7 















95. 













. 0°8 







100. 







0°7. 





1°1 





110 





1°0. . 





0° 4. 











Now we might perhaps suppose that the melting of the ice 

 which undoubtedly at present is more considerable than during 

 the period of maximum glaciation, and therewith following reduc- 

 tion of the salinity of the water have driven Yoldia arctica away 

 from the south-western coast of Greenland. This can, however, 

 not have caused the extinction of Yoldia arctica^ as observations 

 from other places teach us that this small bivalve is an «eury- 

 halin» form which will thrive equally well where the salinity 

 is very slight, e. g. near glaciers and at the outlets of large 

 rivers, and where the water is of very high salinity (more than 

 35 "/oo, ace. to N, Rnipowitsch). 



I have for a long time thought that Yoldia arctica is ex- 

 tinct at the south-western Greenland for the reason that 

 the temperature of the water during a period of the 

 post-glacial time passed the limit at which this 

 bivalve can live, and that Yoldia arctica has had no 

 opportunity of migrating south and recover the lost 

 area afterwards when the conditions again had be- 

 come favourable. 



But if a warmer period had existed it would have left some 

 traces. We know that climatic oscillations cause migrations of 

 animals and we might expect that some southern forms would 

 have appeared and again have retired. 



