KONGL. SV. VET. AKADEMIENS HANnLTNGAR. BAND 32. N:<) 3. 7 



Another organism, the fla.gellate PhoBocystis Pouchetii, appears in the same time as Clia3- 

 toceros decipiens, frequently in great abundance, and has about the same distribution. 

 I therefore include also that organism among the chgeto-species. 



IV. TrichopLailktoil (Sign T). TMs type rules in the western Atlantic and 

 constitutes in the sunimer the plankton of the Irminger Sea. Its origin is doubtful. 

 Typical trichoplankton was gathered in the Bering Sea during the expedition of the Vega 

 and it is an open question whether it spreads from the northern Pacitic to the northern 

 Atlantic or vice versa. In the winter (1897 — 98) the characteristic species of the tricho- 

 plankton appeared as far down to the south as to the south of the Azores, which possibly 

 may be owing to the plankton of the Labrador-current having been conveyed by the 

 south-going branch of the Gulf-stream. In the summer it is confined to the western 

 and arctic Atlantic, but in the winter it spreads to Scandinavia. 



The temperature of the trichoplankton-water varies between 6° and 12° and the 

 salinity amounts to about 34 p. m. 



As the trichoplankton frequently becomes mixed with chajtoplankton and with sira- 

 plankton it is a diflficult matter to make out to what type a number of species really 

 belong. I consider the following as chiefly tricho-organisms: 



Animals. Plants. 



Calanus Jinmarchicus, Ceratium tripos v. nrctica, 



Fritillaria horealis, , Chcetoceros atlantictis, 



Spadella hamata, Coscinodiscus oculus iridis, 



Cyttarocylis denticulata (with the varie- BMzosolenia obtusn, 



ties edentula, media and giganlea), R. semispina, 



Ptychocylis acuta, Tlialassiosira gravida, 



Tintinnus minutus. Thalassiothria' longissima. 



On the coasts, washed by the trichoplankton-water, there originates a peculiar kind 

 of derived trichoplankton, which I have designated as 



Northern ueritic plankton (Sign Ns). This somewhat variable type occurs at the 

 coast of Iceland, in Skagerack and in the fjords of Sweden during the winter, also in the 

 fjords of Norway and on the Norwegian coast-banks, where it becomes in the summer 

 slowly replaced by triposplankton. This kind of plankton seems to invade the coasts of 

 Scotland and Scandinavia twice a year, viz. in the spring in company or in connection 

 Avith the chaitoplankton and in the autumn in connection with the trichoplankton. The 

 detailed study of this kind of plankton will doubtlcss afford very interesting results as 

 different species rule on different coasts. Thus for instance the Asterionella spathulifera 

 abounds in the south coast of Iceland and becomes from thence transported to Scotland 

 and as far southwards as to the coast of Holland. On the coast-banks of Norway 

 Ceratium tripos v. longipes is the ruling species. The Limfjord of Den mark affords par- 

 ticular advantages for the development of some species, as Skeletonema costaium and ChaHo- 

 ceros debilis,^ which remain there for the greater part of the year. 



^ C. G. T. Petersen. Beretnins; fra den diinske biolooiske Station 1898. 



