557 



Færoes then along Greenland, for example I have nol found 

 Gomphonema Aestuarii in Greenland. On the other hånd Achnanthes 

 and Biddulphia which are comraon in Greenland, occur only 

 sparsely along the Færoes, and Striatella gronlandica appears to 

 be absent in the latter place. 



I had been entertaining some hopes that the material would 

 furnish some information of how far certain Diatom-genera are 

 cohfined to certain marinc-algæ, as also whether c er la in 

 genera usually occur toget her. But only a negative result 

 has been obtained, and, in connection with this I shall merely 

 point out that wherever I found Isthmia nervosa abundantly, it 

 usually occurred on Ptilola , and again that it most frequently oc- 

 curred together with Grammatophora , sometimes also with Rhab- 

 donema. I think that I have also been able to observe thai when- 

 ever Diatom -colonies occur on such red algæ which have a flat 

 thallus — on herbarium material they occur as small dark spots — 

 then the colonies usually consisl of Licmophora. 



