PR E FACE. 



THE present work is based exclusively on collections brought 

 home by myself from a journey in Iceland in the summer oF 

 1914. I have not been able to employ the material collected by 

 olhers, the indications of the locaHties on the hibels of the speci- 

 mens being hardly ever exhaustive enough to provide suITiciently 

 accurate information as to the nature of the habitat. Hence, since 

 I have not examined samples collected by others, I have not fol- 

 lowed the method employed in my earlier work »The Freshwater 

 Cyanophyceæ of Iceland« (1923), but have given a list of the indi- 

 vidual samples examined, marked in each case with the collection 

 number. To these numbers I then refer in the systematic list of 

 the species. Aerial Cyanophyceæ being included in Ihe aforemen- 

 lioned work, I give no further systematic list of them, but refer 

 the reader to my previous mention of them (1923). At p. 254 of 

 the same paper will be found a description of my travelling route, 

 and at p. 259 I give an account of the boundaries of the phyto- 

 geographical provinces into which I divide the island, to which 

 account I refer the reader. 



To the Trustees of the Carlsberg Fund, who have granted 

 financial aid for the completion of this work, I beg to express my 

 best thanks. 



22* 



