The scientific Swedish expedition 1898 to Spitzbergen under the direction of Professor 
A. G. Natrsorst paid a particular interest in exploring the plankton of the sea. A great 
number of samples were gathered, among which about 50 were collected by pumping 
the water through a silk-net. These gatherings were all small and have been completely 
examined by me both for animal and vegetable plankton. The other samples, about 100, 
were brought up by the tow-net, partly from the surface and partly from more or less 
considerable depths. As Dr. C. Auriviniius has charged himself with the examination of 
the animals in all the tow-net gatherings, I have examined them for vegetable plankton only, 
with the exception of the radiolarians, which offered a particular interest for my other 
plankton-researches. 
Plankton-types. 
I proposed in 1896! to class the plankton of the Atlantic and its tributaries 
in certain types or formations according to the association of species. For understanding 
the following it will be necessary first to characterize briefly these plankton-types. 
I. Desmo-plankton (sign D). This formation rules in the warmest part of the 
Atlantic, in the Sargasso-sea and in the equatorial current. 
The temperature of the water containing desmo-plankton varies usually between 20° 
and 28° and the salinity is about 36 p. m. 
The organisms belong to a great number of species, many of which are identical with 
those of the Indian Ocean. Among the more characteristic species I can name the following: 
Animals. Plants. 
Clausocalanus furcatus, Trichodesmium, 
Coryceus longicaudis, Pyrocystis pseudonoctiluca, 
C. speciosus, Ceratium fusus var. longiseta (n. v.), 
Eucheta marina, C. tripos var. flagellifera (n. v.), 
Miracia efferata, Ceratocorys horrida, 
Oncea venusta, Gonitodoma acuminatum, 
Setella gracilis, Ornithocercus magnificus, 
Radivlarians (many species). Chetoceros coarctatus, 
C. tetrastichon, 
Climacodium biconcavum, 
C. Frauenfeldii (= C. Jacobi Ct.), 
Hemiaulus Hauckit. 
1 Bih. till K. Sv. Vet.-Akad. Hand. XXII, 3, N:o 5. — A treatise on the phyto-plankton. Upsala 1897. 
