KONGL. SV. VET. AKADEMIENS IIANDLINGAE. BAND 32. N:0 7. 9 



— August in the north of Holland, it may either be a remnant or may have been carried 

 down from Scotland. 



Outside the North Sea the tripos-planhton extends from the northwest of Scotland 

 towards Iceland, but in that region, it is mixed with styli-plankton. 



West of Scotland to about 15° W. the styli-plankton is mixed with Tlialassiothrix 

 Frauenfeldii and 2. longissima, belonging to the tricho-plankton. The region between 

 15° W. and Greenland is almost sterile, which is remarkable, as it is just there that 

 Thalassiotrix longissima usually abounds in the sunnner. 



As stated above, the species which occur in the North Sea are partly remnants 

 from the summer and partly new. The latter can be classed as derived from the north 

 of Scotland and from the English Channel. 



I consider the following as remnants from the summer: 



Ceratium furca and C. fusus, which in the summer occurred in the western North 

 Sea, have noA\' spread över the whole area,. 



C. tripos and C. viacroceros occur now as forraerl}' över the whole North Sea. 



Bacteriastrum varians keeps to the southern pa.rt of the Nortli Sea and approaches 

 Skagerak. 



Clioitoceros curvisetus is, as before, confined to the Skagerak. 



C. densus bas advanced from the southern North Sea towards Skagerak. 



C. didymus is confined to the Skagerak. 



C Schuttii occurs now in such a manner, as to appear to belong to the styli- 

 plankton. This species Avas found in July at Helder, in August and September at Pl}- 

 mouth, in October along the 60° N. from 14" W. to the Shetlands, and reniained in 

 November in the south of the Färöes. It Avas seen also west and east of Scotland. The con- 

 clusion which may be drawn from tliese statements is, that C. Schuttii spreads in the 

 summer through the English Channel along the Continental coast and on the Avest of 

 England to the Färöes and round Scotland into the North Sea, where it ari-ives in the 

 autumn. As this species is common in the Skagerak in the summer it may be assumed 

 that it arrives there along the continental coast. 



Coscinodiscus concinnus, almost absent from the North Sea in the summer, occurs 

 now, together Avith Biddulphia mobilensis and Halosi:)]up,ra viridis, along the Scottish, 

 continental and Danish coasts. The Coscinodiscus and Biddulphia seem to live the Avhole 

 year round the British coasts, but Halosphcera has evidently spread from the south of the 

 Färöes, Avhere it Avas found abundantly in the beginning of November. In all cases these 

 three species have been carried into the North Sea by the south going Scottish cuiTent. 



Guinardia flaccida is found, as before, along the continental coast. 



Rhizosolenia gracillima is confined, as before, to the Skagera-k. 



R. semispina occurs, as before, on the east in rare specimens on\j. 



R. Shrubsolei continues to be rare. 



R. Stolterfothii occurred in September and October both at Plymouth and at Helder. 

 It Avas found also Avest of Scotland, but does not enter into the Scottish current. 



Ceratium tripos var. hucephala is abundant round Scotland and spreads along the 

 57th degree N. into the Skagerak. 



K. Sv. Vet. Akad. Hundl. Baud 32. N:o 7. 2 



