KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 32. N:0 7. 7 



Rhizosolenia obtusa, rare in the Färöe Channel and on the southern coast of Norway. 



R. semis-pina, common off the Filröes, not rare off Scotland, more or less sparingly 

 from the Shetlaiids to Greenland. Rare at Plymouth and on sorae spöts west of Norway. 



T halassiosira gravida, rare off Spitzbergen, in the Färöe Channel and south of 

 Greenland. 



T. Nordenskiöldi, common off the Shetlands, not rare south of Iceland. 



Thalassiothrix Frauenfeldii, sparingly along the 60th degree of lat. to »Reykianäs 

 Ryg»; not seen in the Färöe Channel. 



T. Longissima is not mentioned from the route Shetlands — Iceland, but is found 

 sparingly about 57° 30' N. and 36° W. (along with the styli-plankton). 



Halosphcera viridis has been seen off the Shetlands, but not on the routes Shetlands 

 — Iceland and Shetlands — Greenland ; thus it is probably a remnant from the winter, 

 during which period it occurred south of the Färöes. — Belongs to styli-plankton. 



The above facts point to the conclusion that the northern and arctic forras, which 

 bordered the area of the chaäto-plankton, are derived from south Iceland and the Shetlands. 



3. Styli-plankton was found at a spöt west of Scotland, and, to a small amount, 

 off" the Färöes and Shetlands. This plankton-type appeared contemporaneously at the south- 

 east of Greenland, close above the western slope of the »Reykianäs Ryg». 



4. Tripos-plankton prevails on the west of the Danish peninsula, from whence it 

 passes into Skagerak together with cha?to-plankton and northern neritic plankton. 



3. North Sea in July— August 1897. 



The state of the plankton has considerably changed since the spring. The chceto- 

 plankton has disappeared entirely, and of the northern neritic plankton a small remnant 

 only lingers on the Dutch coast. On the other hand the tripos-plankton has now become 

 the predominant kind in the greater part of the North Sea. Southern neritic plankton pre- 

 dominates in the southern North Sea at Helder and, mixed with styli-plankton, on the west 

 of the Danish peninsula. 



Outside the North Sea the styli-plankton prevails off the Shetlands and Färöes. 



At Plymouth the plankton is now remarkably poor; and the water of 35 p. mille 

 salinity between Norway and Spitzbergen contains styli-plankton very sparingly. 



I now give an account of the species, which constitute the tripos-plankton and the 

 southern neritic plankton and occur simultaneously at this season. 



The animals have, unfortunately, not been cxamined, with the exception of Noc- 

 tiluca miliaris, which is very characteristic of the southern neritic plankton. This organ- 

 ism occurred abundantly at Plymouth from the beginning of July and at Helder from 

 the end of June to the end of September. 



Ceratium tripos occurs at this season in the same region as Chcetoceros decipiens 

 did in the spring. It cannot be assuined that the tripos-plankton has been removed from 

 the region west of Danish peninsula, as the water there had a low salinity in the spring 



