12 v. T. CLEVE. THE PLANKTON OF THE NORTH SEA AND THE SKAGERAK. 



Water of 24,6o to 32,05 p. m. salinity contained as characteristic forras: 



Froto peclata (meridional, iieritic), 



Cyttarocylis denticuhtta (oceanic, boreal and arctic), 



Tintinnopsis campanula (meridional, neritic), 



T. jistularis (neritic, meridional), 



Noctiluca miliaris (in common with the last kind of water), 



Bellerochea malleus (neritic, meridional), 



Rhizosolenia gracillima (oceanic and neritic, euryhaline, meridional). 



Almost all these forms are thus of southern origin. 



Most coininon or generally distributed in all kinds of water ivere the folloioing: 



Oikopleura dioica (meridional, neritic), 

 Acartia Clausii (meridional, oceanic), 

 Anomalocera Patersonii (meridional, neritic), 

 Ca/anus finmarchicus (boreal and arctic, oceanic), 

 Centropages hamatus (boreal, neritic, euryhaline), 

 C. typicus (meridional, oceanic), 



Oithona similis (meridional, oceanic, euryhaline, eurytherm), 

 Paracalanus parvus (meridional, oceanic), 

 ■ Evadne Nordmani (temperate or boreal, oceanic, euryhaline), 

 E. spinifera (meridional, oceanic), 

 Podon intermedius (meridional, neritic), 

 Sagitta bipunctata (meridional, neritic and oceanic), 

 Anvphorella Steenstrupii (meridional, oceanic), 

 Ceratium furca (meridional, oceanic), 

 C. macroceros (meridional, oceanic), 

 C. tripos (meridional, oceanic), 

 ' ' Peridinium, divergens (meridional, oceanic). 



The common species are printed with larger types in the above list. Most coinmon 

 of all were Ceratium macroceros and C. tripos, and as they occurred in all kinds of water, 

 the plankton of the whole North Sea at this time of the year may be classified as tripos- 

 plankton. It is apparent from the last list that the bulk of this kind of plankton is of 

 southern origin, a comparatively small amont only originating in boreal regions. There 

 had thus since April been a complete change of water in the whole North Sea. 



C. The Skagerak, in July. The only samples collected in June in tlie Skagerak 

 were taken at the two stations Mäseskär and Vaderöl>oda. The teraperature of the water 

 varied at these staticms from 13, o to 18, so and the salinity from 18,7o to 32,92. 



The plankton was partly tripos-plankton and the variety of southern neritic-plankton, 

 in which Rhizosolenia gracillima predominates (Nma). If the plankton at both stations 

 Ije compared, a slight difference is apparent. At the more southern station. Måseskär, 



