— 235 — 



S. Sebaldi Reinsch, f. groenlandica Borges, S. megacanthum Lund, 

 S. sp. and Cosmarium sp. 



I am not quite sure with regard to the 

 determination of the Oocystis lacustris; the form 

 observed has 4 cells, about 20/^ long and 14^ 

 broad; the chromatophores are 2 in the cell, 

 but the cell-walls are nearly not incrassated at 

 the apices; it resembles the figure by Borge Fig . 8 . Oocystis la- 

 (Bot. Notiser, 1900, PL 1, fig. 3), from which it custris Chodat (?). 

 differs only by the cells being a little attenuated ( 4o0 /i-) 

 towards the apices (see the fig. 8). 



Staurastrum paradoxum Meyen, var. longipes Nordst., forma is 

 exactly the form figured by Borge (I.e., fig. 4). 



The other Staurastrum which was not rare in the sample, 

 has been identified by me with S. Sebaldi Reinsch. f. groenlandica 

 Börgesen (Ferskvandsalger fra Østgrønland, Medd. om Grønland, 

 XVIII. p. 30, Pl. 2, f. 31). Also Professor Nordstedt to whom I 

 have sent a drawing, thinks that it comes nearest to this form. 

 The length of the cell is 60/j and the latitude is 75//. It differs a little 

 from Börgesen's figure by the more regular disposition of the granules. 



Taken as a whole the plankton from Heiöi has not at all an 

 alpine character, the most characteristic alpine plankton forms e. g. 

 Cyclotella, Stichogloea, Sphaerocystis are completely wanting in the 

 sample; on the other hand Dinobryon and Melosirae are the pre- 

 dominant forms in the lake just as in the northern Central European 

 lowiand lakes ; but the other prominent feature of the lowland lakes, 

 the „ water-flowering" Myxophyceae, which have their maximum in 

 the end of the summer, when the water-temperature is highest, do 

 not occur in the Icelandic plankton sample, which has been taken 

 just at that time of the year. I think we may say that the 

 plankton is like that of the lowland lakes of northern 

 Central Europe and Southern Scandinavia, but much 

 poorer, especially by the want of the summerforms; this 

 also is the case with the climate; it is the climate of northern 

 Central Europe and Southern Scandinavia with regard to the 

 autumn , winter and spring, but the summer is skipped over. It 

 is to be remembered that the lake in question is a lowland lake 

 near the south coast; the case will probably be otherwise for the 

 highland and the North Iceland lakes. 



