F< 



or the hydrographical researches of Pettersson and Ekman/ the North Sea was ex- 

 plored four times during the year 1898, viz.: in March, June, July — August and November. 

 At the same time samples of water were taken for chemical analysis and of plankton 

 for microscopical examination. At the biological stations at Plymouth and Helder samples 

 were collected almost every week during the whole year and also at S:t Vaast la Hogue 

 from June onwards. For this valuable assistance I beg to tender the directors of the said 

 stations, Mr. E. J. Allen, Dr. P. P. C. Hoek and Mr. Eugene Malard my best thanks. 

 Again, at the expense of the Fishery Association of Gothenburg, samples of plankton 

 were collected almost ever}^ week at Måseskär, off the west coast of Sweden, and, though 

 with less regularity, both in the open Skagerak and along the Swedish west coast from 

 Vinga to Väderö. 



'ö^ 



1. The North Sea in March 1898. 



The prevailing plankton type is the chceto-plankton, which extends from the British 

 east coast, between the Firth of Tay and Newcastle, to the south-west of Norway and the 

 west of the Danish Peninsula. to about 55° 30 N., i. e. above the 100 metre plateau. It 

 also occurred south of the Dogger Bank, above the depression of the bottom at this place. 



The cha?to-plankton region approximately coincides with the southern part of the 

 region of the water with 35 p. mille salinity, as marked on the hydrographical map of 

 Pettersson and Ekman.^ The northern part of the North Sea, or above the 200 metre 

 plateau, was poor in plankton or almost sterile, containing Calanus finmareliicus sparingly. 

 Above the great depth between the 200 metre plateau and the west coast of Norway the 

 water was extremely poor in plankton, containing hoAvever some rare specimens of a 

 number of interesting radiolarians, Ceratium arcticum and Coscinodiscus oculus iridis. 



In the spring of 1897, when chteto-plankton also prevailed above the 100 metre 

 plateau, the area of this plankton type was bordered by a band containing arctic and 

 northern forms. This was not the case in 1898. The southern part of the cha^to-region^ 

 from Newcastle to Skagen, in 1898 contained Coscinodiscus concinnus more or less abun- 

 dantly; and above the edge of the 50 metre plateau as well as above the Fisher Bank 

 Rhizosolenia styliformis was met with, more or less sparingly to about 1° 30 E. and also 

 above the depression south of the Dogger Bank. 



1 Bih. till K. Sv. Vet.-Akad. Handl. Vol. XXV, II, N:o 1. 1899. 



