8 ]'. T. PLEVE. PLANKTON, COLLECTED BY THE SWEDISII EXPEDITION TO SPITZBERGEN. 



The temperature of the water with northern neritic plankton varies in Skagerak 

 from about 4° to 7° and the snlinity is about 32 — 33 p. m. 



As species constituting the northern neritic plankton we name the following: 



Animals. Plants. 



{Acartia longireniis), Asterionella spathulifera, 



{Calanus finmarchicus), Biddulphia aurita, 



{Centropages hamatus), Chcetoceros dehilis, 



{Pseudocalanus elongatiis), C. diadema, 



(Temora longicornis), C. scolopendra, 



Tintinnopsis beroidea, C. teres, 



T. ventricosa. Coscinodiscus polyehordus, 



Leptocylindrus danicus, 

 Skeletonema costatum, 

 Thalassiosira gelatinosa, 

 ThalassiotJirix Frauenfeldii, 

 Ceratiutn tripos v. longipes, 

 Gonyaulax spinifera, 

 Peridinium depressum. 



V. Sira-plailkton (Sign Si) rules along the coasts of Greenland and in Baffins Bay, 

 or in the Arctic Ocean properly, where it constitutes the plankton of the water with 

 raelting drift-ice. As it touches the trichoplankton it becomes frequently mixed with it, 

 so that the distinction of what species belong to one or the other is a matter of difficulty. 

 The water with sira-plankton has lower temperature than the trichoplardrton- water and 

 less salinity, about 32 — ^33. This type might be considered as a kind of neritic plankton, did 

 not the most characteristic species, Thalassiosira Nordenskiöldii, at certain periods occur 

 in wide areas north of the Kära Sea and between Spitzbergen and Finmarken. Typical 

 sira-plankton is almost free from animals and contains as its most characteristic species 

 Thalassiosira Nordenskiöldii, Fragilaria oceanica, Lauderia fragilis, ChcBtoceros furcellatus 

 and C. socialis. It is frequently mixed with some northern neritic forms as Chcetoceros 

 dehilis, C. diadema, C. scolopendra, Coscinodiscus oculus iridis, Biddulphia aurita,, Tha- 

 lassiosira gravida etc. 



This kind of plankton appears in Skagerak usually in February and March. 



Along the coast of Greenland the sira-plankton becomes mixed with a number of 

 neritic forms and such a derived sira-plankton I have distinguislied as 



Arctic neritic plankton (sign Ng). This kind of plankton contains, besides the 

 species of sira-plankton, the following: 



Åmphiprora liyperborea, Eucampia groenla.ndica, 



Achnanthes tceniata, Fragilaria. cylindrus, 



Chcetoceros septentrionalis, Navicula septentrionalis, 



Coscinodiscus bioculatus, Nitzschia frigida, 



C. hynlinus, Pleurosigma Stuxbergii. 



