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



43 



that had its flowering-season in January. There is f urther a notable difference in the råtes 

 of frequency of Leptocylindrus, this diatom being, if not rare, yet very much more spar- 

 sely represented than may be the case in other spring seasons in these waters. Its low 

 maximum of 18,000 ind. per 1 is found near the water-limit, at 10 m. Among its ordi- 

 nary companions, Rhizosolenia semispina is not missing, but the species of Chaetoceras 

 seem to vary with the different years, Ch. contortum being this time the leading form. 

 Its frequency does not, however, surpass 5,000 ind. per 1 in the layers where it is multi- 

 plying; near the bottom there are 6,600 ind. per 1. It may be remembered that quite other 

 species of Chaetoceras were dominating in April 1913, viz. Ch. debile, Ch. decipiens and 

 Ch. sociale. 



Also concerning the disc-formed diatoms of the winter-formation, there are notable 

 differences to be observed between the two April-series. That of 1913 was almost free 

 from Thalassiosirae etc, whereas in 1914, these algae are still regularly spread from 20 m 

 downwards. To the, downwards rapidly increasing, masses of Sceletonema in 1914, there 

 is no parallel in 1913. These differences cannot, anyhow, be explained by the present 

 hydrographical conditions, that are most similar both years in the lower water-masses, 

 but fresher and colder to a deeper limit in 1913 than in 1914. They must be caused by 

 earlier differences in the quantity and distribution of the winter-diatoms, that are, how- 

 ever, known only from the latter year. 



Table 66. 8. Skag. 0. 57° 41' N., 11° 24' E. 17. IV. 1914. 



-C 

 *> 



a, 



o 

 C 



<D o 



a. 

 S £ 



a> 3 



o 



o 

 o 



>> 



'a 



"3 

 m 



>> 



49 



ro 



c 

 o 



Q 



'5 

 -3 



o 

 ö 



s 



>> 



o 



.5 



'C 



0) 



Peridiniales 



total 



numbers 



s 



3 



■5 

 o 



a 



s 



8 

 © 

 o 



cS 



Protozoa 



total 

 numbers 







7,61 



21,27 



16,60 



S40 





180 



2,140 



1,200 



2,110 



3,490 



10 



6,54 



30,73 



24,14 



1,500 



150 



450 



4,600 



250 



2,900 



4,650 



20 



6,08 



31,44 



24,76 



600 



250 



200 



3,200 



100 



350 



2,250 



30 



5,57 



32,41 



25,58 



300 



50 



170 



1 ,420 



350 



250 



1,150 



40 



5,59 



32,52 



25,67 



300 



80 



220 



1,160 



320 



60 



1,120 



50 



5,25 



33,03 



23,11 



400 



20 



140 



1,060 



220 



240 



740 



60 



5,17 



33,75 



26,67 



200 





80 



540 



480 



200 



1,300 



80 



5,10 



33,95 



26,85 



200 





60 



620 



120 



80 



40O 



90 



5,11 



33,96 



26,85 









250 





100 



300 



The Peridiniales and Protozoa also thrive better at some metres' depth, than in the 

 very surface-current. Only Mesodinium makes an exception. From the table will also 

 be found, that the named organisms do not decrease downwards at so rapid a råte, as usual. 



S. Skag 5 (p. 44). At about 10 m, there is a mixture layer, where the diatoms of the 

 Leptocylindriis-iorm&tion are particularly numerous, to be cut off short a little below. This 

 feature is by no means rare and is easily explained by the råte of sinking being abruptly 

 lessened, when meeting with a new, denser kind of water. The undercurrent is in hydro- 

 graphical respect very like the bottom water of S. Extra II, and no doubt both waters 

 are of the same origin, though that at the mouth of the Kattegat has been more mixed up. 



