4 P. T. CLEVE. THE PLANKTON OF THE NORTH SEA, THE ENGLISH CHANNEL, AXD THE SKAGERAK. 



As no sainples of plankton have been collected above the 50 metre plateau nothing 

 is knoAvn about the plankton of the southern Xorth Sea. 



The tripos-plankton, prevalent during the past summer, autumn, and winter above the 

 100 metre plateau, occurred in March 1898 chiefly in the eastern part of the Xorth Sea 

 and Avest of the Danish Peninsula, and there more or less intermingled with chieto and 

 northern neritic plankton: the last-named was present during the winter in the Skagerak. 



Oriffin of the chaeto-plankton. I propose in another paper to treat of the origin of the 

 cha?to-plankton, and it will there be shown that the diatom, Chcetoceros decipiens, which 

 constitutes the principal mäss of the chaito-plankton, belongs to the west Atlantic area, 

 or to the cold southwards current along the American coast, and that it is thence con- 

 veyed by under-currents across the Atlantic towards the Azores and the European coast. 

 In the month of November, when the superficial strata of the Atlantic are driven away 

 — or rather become mixed with those beneath — the species above-mentioned appears at 

 many points between the Newfoundland Banks, the Azores and the mouth of the English 

 Channel. It multiplies during the winter and is conveyed in the spring towards Iceland, 

 the Färöe Channel and into the Xorth Sea, whence it spreads towards Spitzbergen. 

 Other species of the west Atlantic area, which accompany Chcetoceros decijnens across the 

 Atlantic, such as Calanus finraarchicus, Thalassiothrix longissima and Ceratium arcticum, 

 die sooner or later in water of so high a salinity as 35 p. m. 



Some species of the temperate Atlantic, such as Onccea minuta, O. conifera, Oithona 

 plumifera, O. similis, Collozouni inerme, frequently follow the chajto-plankton on its way 

 towards the north. 



Species which accompany the Chaetoeeros decipiens into the North Sea. The fol- 

 lowing species occuiTed in the Xorth Sea över the whole chaeto area or at least in its 

 western parts. Some of them are of southern origin, or belong cssentiallv to the styli 

 and desmo types, others come from northern regions and from Scotland. 



Species of sonthern origin 



Acartia Clausii, 

 Microsetella atlantica, 

 Oithona similis, 

 Sagitta bipunctata, 

 Globigeiina hulloides, 

 Acanthometron quadrifolium, 

 Halosphcera viridis. 



Species of northern origin 



Calanus finmarchicus, 



Metridia h ibern ica , 



Pseudocalanus elongatus, 



Temora longicornis, 



Cyttarocylis denticulata, 



Gonyaulax spinifera, 



Chcetoceros borealis var. Brighticellii, 



Coscinodiscus oculus iridis, 



C. polychordzis, 



Rhizosolenia semispina. 



Biddulphia mohilensis and Strejytotheca Thamesis come in all probability from the 

 coasts of Scotland. 



