82 



ERNST ØSTRUP 



Forms found in 100 samples or more. 



Characterising forms in 10 samples or more. 



Meridion circulare. . . , 

 Diatoma hiemale . . . . 

 Synedra Ulna danica. 

 Melosiræ sp. diversæ . 

 Synedra Ulna typica . 



50 

 43 

 41 

 37 

 36 



6 Epithemiæ sp. diversæ . . 



7 Cymbellæ sp. diversæ . . . 



8 Fragilariæ sp. diversæ... 



9 Ceratoneis Arcus 



22 

 17 

 16 

 10 



This table shows that the forms most characteristic to the 

 Icelandic flora of fresh-water diatoms are: Meridion, Diatoma, Synedra 

 and Melosira. Comparing the two lists it further appears, that the 

 fact of a form being met with in a great number of samples not 

 necessarily means that it is generally characterising: for inst., Navicula 

 radiosa marked no. 2 in the first list only characterised two samples; 

 Cymbella ventricosa, Pinnularia viridis, Gomphonema subclavatum 

 each only one sample, while Pinnularia borealis and Hantzschia 

 amphioxys did not characterise any. 



