PLANKTON-TYPKS. 



NOKTHKRiX NKHITIC i'LANKTOX 



15 



It is remarkable that many of these species are also Baltic and 

 not a few circumpolar. 



I distinguish as a particular class a number of plankton forms 

 which are not strictly arctic, but boreal, and occur off Iceland and 

 the Faroes, in the Irminger Sea and in the K. Greenland Current. 

 The mean temperature of the water in which these forms occur is 

 as a rule higher than for the strictly arctic si)ecies. A number of 

 these forms constitute what 1 have called Northern n er it ic plankton, 

 others fall under the Sira-plankton . It is remarkable that such a 

 considerable percentage of these forms occur in the northern Pacific. 

 There are also among these forms some Baltic species. 



The following list contains such boreal forms: 



Boreal species. Ns. 



Limits 

 Lat. N. 



Limacina retroversa 71° — 41° 



Arachnactis albida 62° — 56° 



Anomalocera Patersonii 73° — 50° 



Centropages hamatus 70° — 50° 



Metridia hibernica 69° — 42° 



Temora longicornis 70° — 40° 



Amphorella subulata 65° — 40° 



Godonella ventricosa 66° — 36° 



Tintinnopsis beroidea 63° — 34° 



Dinophysis acuta 73° — 42° 



Gonyaulax spinifera 65° — 34° 



Hexasterias problematica 66° — 51° 



Astorionplla japonica 63° — 50° 



Biddulphia aurita 75° — 52° 



Ghaetoceros cinctus 65° — 60° 



G. constrictus 63°— 39° 



G. debilis 74°— 40° 



G. hiemalis 76°— 45° 



G. laciniosus 70° — 43° 



G. scolopendra 66°— 40° (21°) 9.5 



(^oscinodiscus concinnus 69° — 40° (7 



C. excentricus 64°— 32°(21°) 9 



