KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 57. NIO 7. 



45 







Table 69 



s. 



Skag 



. 6. 57° 56' N., 



9° 40' E. 18. 



IV. 



1914 







CD 



CD o 



£ £ 



CD 3 



o 

 o 



o 



>» 

 'c 

 ~£ 



>> 



'w 



C 



CD 



Q 



C3 



t- 



' 3 „ 



O cS 



2? ^ 



8 = 



3 



Coseinodis- 



cus con- 



cinnus 



.2 a 



g JU 



JS ^ 



^H CO 



03 



'3 = 

 o 



cS 

 fl;- 



•9 5 



2 ° 

 -2 ff 



'SM 

 o 



■ <o 



.5 u 



^5 



c; o3 



O T! 



-ta 



CL «> 



Biddulphia 

 sinensis 



Rhizosolenia 



hebetata 

 f. semispina 



Rhizosolenia 

 Stolterfothii 



Rhizosolenia 

 fragilissima 



Chaetoceras 

 contontum 



Diatoms 



total 

 numbers 







6,54 



27,45 



21,57 











40 



1,640 



320 







180 3,680 



10 



6,04 



34,65 



27,29 



380 





1,200 



720 



60 





40 



860 



280 



4,580 



20 



6,04 



34,65 



27,29 



240 





1,280 



410 



20 



80 



40 



620 



220 



220 4,230 



30 



6,04 



34,63 



27,28 



320 





400 



430 



130 



40 



(10) 



1,000 



330 



2,020 



5,740 



40 



6,05 



— 



— 



150 





440 



680 



70 



60 



15 



1,930 



230 



1,150 



5,545 



50 



6,06 



34,63 



27,28 



180 





600 



920 



20 



80 



20 



1,260 



20 



1,960 



6,420 



80 



6,06 



34,65 



27,29 



160 





280 



440 



70 



40 



10 



500 



30 



380 



2,650 



100 



6,04 



34,72 



27,35 



60 





360 



560 



160 





(40) | 10 



1,400 





220 



4,180 



Avei 

 11 



age-nu 

 )0 ni 



mbers 



10— 



214 







594 



76 



43 



12 14 



1,081 



159 





4,914 



The features of this station are particularly interesting. From a thin surface-layer 

 of some few metres, carrying off from the coastal regions a scanty vegetation of Lepto- 

 cylindms and Rhizosolenia semispina, there is a sharp transition to a most uniform water, 

 filling all the rest of the boundary, from less than 10 m depth to the bottom. The hydro- 

 graphical data of this water are almost totally unchanged all through t hat column of 90 

 m, the temperature staying at 6°,o4, the salinity at 34°,65. This suggests a large water- 

 mass having been mixed well through, before having burst suddenly into Central Skager 

 Rak, where it must have driven completely away the waters previously filling that basin, 

 thanks to its high salinity. To judge from the quite unchanged nature of this water even 

 near its upper limit, the invasion must have occurred a very short time before the samples 

 were taken; if so, we may expect to find also a uniform plankton, the time having been 

 insufficient for a noteworthy multiplying on spöt. This supposition is confirmed by 

 the plankton-lists; and table 69, that gives the numbers for some more remarkable forms, 

 shows how an average number of frequency can be calculated for most species through 

 the whole column. Likewise, the total amount of the diatoms constantly keeps at about 

 5,000 ind. per 1, with small divergencies. 



If we now consider the nature of this uniform plankton, we find it quite different 

 as w r ell from that, taken simultaneously at the neighbouring station Skag. 5, as from 

 the vegetation, registered for the Central Skager Rak in April 1913. There need only 

 be pointed at the high amount of markedly southern types, as Guinardia flaccida, Rhizo- 

 solenia Stolterfothii, Rh. fragilissima, while Coscinodiscus concinnus is missing and Bid- 

 dulphia sinensis very rare, to make it clear that the North Sea-currents near Jutland (S. 

 Skag. 5) and in the central part of the Skager Rak (S. Skag. 6) are of a quite different 

 origin. By studying the great review concerning the distribution of the plankton-dia- 

 toms given by Mr Ostenfeld in 1913 we may come to the following conclusions. 



By his maps, Pl. LXXI and Pl. LXIX, is sufficiently shown, that as well Rhizo- 

 solenia Stolterfothii as Guinardia have their centres of distribution in the English Chan- 

 nel, while Biddulphia sinensis, for which species Mr Ostenfeld does not give any map, 



