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It will be seen from the table, that the tarn near Velbestad, 

 which is the largest of the five, differs considerably from the others 

 by the predominance of diatoms. I found Fragilaria capucina pre- 

 dominant and other forms not rare; connected herewith I noticed 

 the occurrence in the sample of a large quantity of bottom diatoms, 

 e. g. Pinnularia major Kütz., P. lata Bréb., Bhopalodia gibba (Kütz.), 

 O. Müll., Cyclotella antiqua W. Sm., Surirella ovalis Bréb., Cymbella 

 cistula (Hempr.) Kirchn., Gomphonema acuminatum Ehbg. v. coronata 

 Ehrbg., etc. ; also some few specimens of Diatoma hiemale (Lyngb.) 

 Heib. have been found. From this fact we may conclude that the 

 bottom of the tarn houses diatoms in abundance. Of the other 

 organisms the Peridinium Willei is the most numerous; in Mr. 

 Börgesen's and my paper cited above I have made some remarks 

 concerning this interesting form (1. c. pp. 622—623); I had at that 

 time not seen it in so large quantities as in the samples now exa- 

 mined; and it appears from the table that it has been found in 

 all live tarns and in abundance in the three of them; it seems to 

 me as if this form should be taken as a characteristic organism 

 of small lakes in northern countries with low summer-temperature. 



J ) Lemmermann, E., Beitr. z. Kennt, d. Planktonalgen. Ber. Deutsch. Bot. 

 Gesellsch., 1900, p. 515. PI. XVIII, figs. 17—18; Botan. Notiser, 1903, PI. 3, 

 figs. 1—2; Forschungsber. a. d. Biolog. Station zu Plön X, 1903, p. 164, figs. 7. 



2 ) The resting spores of Dino bry on-species are very often found in slides 

 with cleaned and ignified diatoms. 



Fig. 9. Dinobryon sociale 

 Ehrbg. with resting spore. 

 ( 450 /i). 



Another of the common plankton forms 

 in the sample from Velbestad is a D i n o b r y o n, 

 which I have identified with D. sociale Ehrbg., 

 as Lemmermann l ) has taken this name ; as 

 will be seen from my fig. 9, the form comes 

 nearest to his figure 7 a in „Forschungsber. 

 a. d. Biolog. Station z. Plön" X, 1903, p. 184, 

 but it differs by having more angulated houses. 

 It occurred with resting spores, which besides 

 were common in slides of the cleaned dia- 

 toms' 2 ). The same form also occurred in 

 one of the tarns in Kirkebörejn, but not so 

 abundant. On the other hand I found some 

 few colonies of another Dinobryon in a 

 sample, taken in another tarn in Kirke- 

 börejn at about 200 M. over the sea. This 



