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Part III. — Fifteenth Annual Report 



always in company with southern forms, and it belongs to tripos- and 

 didymus-phmkton. 



3. G. tripos var. arctica, Ehb. = G. tripos var. labradorica, Schiitt, 

 fig. 3, is abundant in Baffin's Bay and the Labrador current. The form 

 figured by Claparede and Lachman is remarkable for the coarse apiculi 

 on the horns and the tail. It has not yet been found with certainty 

 in the Kattegatt and Skagerak. 



4. G. tripos var. longipes, Bail = tergestina, Schiitt, arctica, Aur, fig. 2, 

 was rarely found in the ' Research ' samples ; it occurs in the winter 

 abundantly in the Kattegatt and Skagerak. 



5. C. tripos var. horrida, CL, fig. 4, resembles the var. longipes, but is 

 remarkable for the spines on the horns and the tail. Occurs, although 

 rarely, in most of the 'Research' samples. 



6. G. tripos var. bucephalus, CI., fig. 5, was not found in the 

 ' Research ' samples, but this summer in the collections of the Swedish 

 expedition to Spitsbergen, as well as in a sample taken at the end of 

 October in the middle of the North Sea. 



Peridinium divergens, Ehb. (Stein, Inf., PI. X. figs. 1-5). 

 Pyrophacus horologium, Stein (Inf., PI. XXIV.). 



C. SlLICOFLAGELLATES. 



Dictyocha fibula, Elib., extremely rare in the mixed sample. 

 Dictyocha specidum, Ehb., rarely in No. 11. 



j 



D. Chlorophyllacean. 

 Halosphoera viridis, Schmitz, rare in several of the samples. 



Results. 



In a paper published this 1896 (in Bih. K. Sv. Yet. Akad. Handl., Bd. 

 XXII. 3, No. 5), I have distinguished in the Skagerak and Kattegatt 

 four different types of plankton, viz. : — 



I. Tripos-planldon, characterised by abundance of crustaceans and 

 cilioflagellates, but usually a scarcity of diatoms, among which Coscino- 

 discus concinnus and Rliizosolenia gracillima are the most important. 

 This kind of plankton rules at the west coast of Sweden in the summer, 

 and there are reasons for believing it to be derived from the northern or 

 southern North Sea. 



II. Didymus-plankton (Sign N), characterised by Ghoetoceros didymus, 

 G. Schuttii, G. curvisetus, G. laciniosus, Ditylum Brigldwellii, Leptocy- 

 lindrus danicus, Skeletonema costatum, Eucampia Zoodiacus, &c, all 

 species belonging to the coast-plankton of the English Channel, west 

 Scotland, and continental coasts of the North Sea. It appears in the 

 Skagerak and Kattegatt in the autumn, and comes no doubt along 

 the west coast of Jutland and from Norway. 



III. Tricho-plankton (Sign T), characterised by abundance of diatoms, 

 the most important being Thalassiothrix longissima, Rliizosolenia 

 semispina, Ghoetoceros atlanticus, G. borealis, G. decipiens, &c, species 

 abundant in the western part of the Atlantic, south of Iceland. It 

 arrives to Sweden in January and February, usually mixed with the 

 following kind : — 



IV. Sira-plankton (Sign Si), characterised by an abundance of diatoms, 



