8 YP. T. CLEVE. PLANKTON, COLLECTED BY THE SWEDISH EXPEDITION TO SPITZBERGEN. 
The temperature of the water with northern neritic plankton varies in Skagerak 
from about 4° to 7° and the salinity is about 32—33 p. m. 
As species constituting the northern neritic plankton we name the following: 
Animals. Plants. 
(Acartia longiremis), Asterionella spathulifera, 
(Calanus jinmarchicus), Biddulphia aurita, 
(Centropages hamatus), Chetoceros debilis, 
(Pseudocalanus elongatus), C. diadema, 
(Temora longicornis), C. scolopendra, 
Tintinnopsis beroidea, C. teres, 
T. ventricosa. Coscinodiscus polychordus, 
Leptocylindrus danicus, 
Skeletonema costatum, 
Thalassiosira gelatinosa, 
Thalassiothrix Frauenfeldii, 
Ceratium tripos v. longipes, 
Gonyaulaz spinifera, 
Peridinium depressum. 
V. Sira-plankton (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 
melting 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 trichoplankton-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 Nordenskidldii, at certain periods occur 
in wide areas north of the Kara Sea and between Spitzbergen and Finmarken. Typical 
sira-plankton is almost free from animals and contains as its most characteristic species 
Thalassiosira Nordenskildi, Fragilaria oceanica, Lauderia fragilis, Chetoceros furcellatus 
and C. socialis. It is frequently mixed with some northern neritic forms as Chetoceros 
debilis, C. diadema, C. scolopendra, Coscinodiscus oculus tridis, Biddulphia aurita, Tha- 
lasstosira 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 distinguished as 
Arctic neritic plankton (sign Ng). This kind of plankton contains, besides the 
species of sira-plankton, the following: 
Amphiprora hyperborea, Eucampia groenlandica, 
Achnanthes teniata, Fragilaria cylindrus, 
Chetoceros septentrionalis, Navicula septentrionalis, 
Coscinodiscus bioculatus, Nitzschia frigida, 
C. hyalinus, Pleurosigma Stuxbergii. 
