KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 57. N:Q 7. 



11 



ton is at a quite ruling degree very equally distributed through this thick layer, diatoms 

 as well as peridinians. There is one interesting exception only: Guinardia fluccida must 

 have been capable of a considerable multiplying at a depth of 30 — 40 m, where the light 

 is insufficient for a noteworthy development of most forms, and this propagation must, 

 from all to judge, have followed in quite a short time. There is a second, very sharp 

 hydrographical limit near the surface, but this time a limit of salinity only, the more 

 diluted surface-water spreading in a thin cover över a very salt water of 34,6 — 34,7 °/ „, 

 t hus salter than the underlying one. The fact that this water has the same high tempe- 

 rature as the fresher layer above it, and contains an almost pure, comparatively rich vege- 

 tation of Rhizosolenia gracillima, suggests the thougt that it has been stationary in the 

 basin for a rather long time and probably was cut in two, I would say, by the inbursting 

 middle, still very homogenous layer. The tiny diatom, mentioned above, thus proves 

 to be a more oceanic form, evidently thriving better in a salt open sea-water than near 

 the coasts, in spite of the better nutritious supply from the latter. Where, then, does the 

 uniform water between 30 and 60 m come from? To judge from the tolerably rich plank- 

 ton with quantities of such a litoral, heavy diatom as Paralia, it must be a coastal water 

 of southern origine, thus what may be shortly called a southern bank- water, previously 

 known to immerge into the Skager Rak in late summer. Its leading forms have also for 

 a great part been referred by Cleve to lus Nm (southern neritic )type. The relatively 

 low temperature indicates a deep-water current. 



Also Rhizosolenia gracillima belongs to this southern neritic-association, but hardly 

 as a leading form, staying far behind the both dominating diatoms, Guinardia and Paralia. 

 There is, of course, a possibility, that the maximum of Rhizosolenia at 10 m has developed 

 from germs, risen from this same association, whose scanty rests we have already traced 

 at the inner stations. 



As the immigrated southern-neritic association is seldom met with in a more pure 

 and genuine form, I here will enumerate its most important diatoms in accordance with 

 tlieir frequency at this season: Guinardia flaccida, Paralia sulcata, Rhisosolenia alata f. 

 gracillima, Rh. Shrubsolei, Pleurosigma planctonicum n. sp., Navicula distans. 





Ta 



ble 8 



. s. 



Skag 



. 6. i 



57° 56' N., 



9° 40' E. 



16. 



VIII. 1912. 





a, 



O 



Q 



Tempera- 

 ture °C. 



o 

 o 



>> 



"a 



n 

 C 



Q 



el 



.2 "5 

 £ s: 



6S & 



t- m 



© s 



O 3 



.2 £ 

 fe ° 



© cg 



° s 



s 



Ceratium 

 furca 



Ceratium 

 longipes 



Ceratium 

 tripos 



Ceratia total 

 numbers 



Prorocent- 

 rum micans 



'g 



Diplopsalis 

 lenticula 

 f. minor 



Peridiniales 



total 



numbers 







15,39 



30,28 



22,29 









20 



20 



160 



200 





20 





340 



10 



15,39 



34,58 



25,58 













40 



40 









70 



20 



14,66 



34,69 



25,76 













10 



10 





10 



20 



85 



30 



11,10 



34,34 



26,27 





70 



40 





340 



60 



520 





20 



50 



660 



40 



11,06 



34,34 



26,27 





30 



20 



10 



300 



40 



430 





20 





470 



50 



10,89 



34,34 



26,31 



20 



30 



10 



40 



190 



50 



340 





20 



30 



450 



60 



10,81 



34,36 



26,33 









70 



270 



90 



460 







30 



540 



80 



8,05 



34,69 



27,04 











30 





30 







£0 



100 



100 



6,85 



34,94 



27,43 



















20 





40 



