16 P. T. CLEVE, THE PLANKTON OF THE NORTH SEA AND THE SKAGERAK. 



Eucampia zodiacus c, 

 Guinardia flaccida c, 

 Lauderia annulata rr, 

 Lithodesiniwn undulatum rr, 

 Rhizosolenia calcar aris + , 

 R. ffraciUima + , 

 M. Shrubsolei r. 

 R. Stolterfothii + , 

 R. styliformis c, 

 Stephanopi/wis turris c. 



The names of species, aboiit which it is at present uncertaiu whether thcy are soiithcni or northern, 

 have been cnclosed iu brackets. 



The prevailing number of species belong to the r/'/c/?/?u?<s-plankton and are chiefly 

 of Southern origin. Among these forms there occurred abundantly in the southern North 

 Sea the diatom Rhizosolenia styliformis, Avhich is in niy opinion an oceanic species of the 

 temperate Atlantic. That proves that the bank-Avater off the Continental coast had been 

 niixed with Atlantic water, entering through the English Channel. 



B. The Skagerak at Vinga. The Government steamer »Svensksund» collected on 

 the '21th of November at Vinga two samples of plankton, one from the surface and one 

 at the depth of 30 m. The surface water had the temperature 6,02 and the salinity 

 21,01 and belonged thus to the Baltic Current. The water at 30 m. was warmer (tem- 

 perature 9,5) and had the salinity 32,75. The latter kind must thus be classified as bank- 

 water. The microscopical examination of the plankton proved that the Baltic Current 

 contained tripos-, but the bank-water c/{t/?/»i«,.s-p]ankton. The water of the Baltic Current 

 derived consequently in part from the Baltic and fresh water from the coast and in pai't 

 from tlie North Sea, above the 100 ra. plateau of the bottom. The bank-water on the 

 contrar)', originated from the southern North Sea, above the 50-metre plateau of the 

 bottom. 



C. The Skagerak at Måseskär and Väderö. Samples collected at the stations Måse- 

 skär and Väderöboda were taken in water of the temperature 8,3 to 5,9 and of the sali- 

 nity 20,61 to 28,82. The plankton was, on both places, essentially of the same kind, very 

 rich in forms, not less than 73 different species belongiiig partly to the trijjos- and 

 partly to southern and northern neritic plankton, the two latter constituting together Avliat 

 I have called didyniusplankton. 



December 1900. 



The Skagerak. Samples were collected at the stations Måseskär and Väderöboda 

 in Avater of the temperature 6,0 to 3, o and the salinity 21,33 to 30,94. The plankton was 

 less abundant than in November but rich in species, 78 different forms having been noted. 

 The plankton belonged to tripos- and c/u/y/xn.s-plankton, as in the preceding month, but 

 the relative abundance of the species seemed to have been somewhat altered. 



