MicroplanJcton from the Finnish Waters during the Month of May 1912. 9 



Coscinodiscus lacustris occurred in small quantities at every station fairly equally 

 distribated. The greatest number was 1520 cells pr. litre (station F 23, mètres). At 





V,-., 





Fig. 5. Coscinodiscus lacustris. 



iioo 



a. Cells in i'ront-view. 



1250 



b. Cells in side-view. — . — 



some of the stations the largest quantities were found in the mitldle and 

 layers (F 41, F 50. F 61, F 74). On the contrary at station 

 F 30 the maximum number was found at the depths of 5 10 

 mètres. Station F 23 besides having the greatest number of cells 

 in the surface water (1520 cells pr. litre) also produced a se- 

 condary maximum (1440 cells pr. litre) at the depths of 40 — 50 

 mètres. 



This relatively rieh occurrance towards the deep layers can 

 naturally be explained, when we consider the tact, that Coscino- 

 discus lacustris is a heavy form, which will easily sink. 



deeper water- 



Fig. 6. Coscinodiscus sp. 

 1050 



1 "- 



Coscinodiscus sp. 



(Fig. g. , 



Hère and there a little thick-walled Coscinodiscus with cup-shaped valve was to be 

 found. The pores being reinote at the central part of the valve approached each other 

 towards the edge. The margin of the valve was supplied with hue radial stripes. 



A few spécimens of this species occurred at. stations F 74 and F 61. 



N:o 5. 



