8 P. T. CLEVE. THE PLANKTON OF THE NOKTH .SEA AND THE. SKAGEKAK. 



Chcetoceros atlanticus, 

 C. borealis, 

 C. contortus, 

 C. scolopendra, 

 Coscinodiscus concinnus, 

 C. radiatiis, 

 C- oculus iridis, 

 Skeletonenia costatum. 



Of species found in the bank-water a few rare specimens only are of southern 

 origin, but the boreal and arctic forms are enormously pre^'alent. It is thus proved that 

 the bank-water at the end of the winter becomes at fii-st populated by arctic and boreal 

 species, which disappear or diininish during the sunimer, when the sj^ecies of southern 

 origin, which arrive in the spring, increase. 



Species which occurred as often in the 34 p. m. water as in the bank-water Avere 



Acartia Clausii, Chcetoceros decipiens, 



Centropages hamatus, C. teres, 



Paracalanus parvus, LeptocyJindrus danicus. 



Ceratium furca, 



C. fusus, 



c. longipes, 



Dinophysis acuta, 



Peridinium pallidum. 



B. The Skagerak. The plankton was, to judge from the samples collected at 

 Måseskär, on the whole poor. Most arctic forms had disappeared. The only forms of 

 any importance were Chcetoceros borealis, C. contortus, C. decipiens, PJiizosolenia semispina, 

 B. setigera, l^halassiothrix Frauenfeldii and Divobryum. 



May 1900. 



A. The North Sea. I have received three samples only from the Northeast of 

 Scotland 58°— 59° N. 1' E — 2' W., all collected in water of 35,32 p. m. sal. and the tem- 

 perature 6,7 to 7, c. These samples contnined the following species: 



OikopÅeura dioica -\-, Sagitta bipunctata -{-, 



Calanus Jinmarcincns c, Cyttarocylis dentindata -j-, 



Centropages hamatus r, Ceratium furca r, 



Oithona similis r, Chcetoceros decipiens -f-, 



Pseudocalanus eJongatus c, . Rhizosolenia styliformis c, 



The plankton was thus styli- and tricho-plankton, containing some neritic forms. 



