THE FRESH-WATER CYANOPHYCEÆ OF ICELAND 253 



and over a well at OndverSarnes under the name of Rhodochorton 

 islandiciim. 



In 1902 G. S. West gave a list of the species he had found in 

 a number of samples collected at the hot springs in Iceland by 

 A. W. Hill. He mentions 5 species of Chiorophyceæ and 16 species 

 of Cyanophyceæ. These are all mentioned in the present work. He 

 introduces a new species Aulosira thermalis which 1, however, must 

 assume to be identical with Hapalosiphon laminosiis (Cohn) Hansg. 

 (See below under this species). 



The first information regarding the phytoplankton of Iceland 

 was given by Ostenfeld (1904). He examined a plankton sample 

 from a small lake in South Iceland and found that it contained 6 

 Chiorophyceæ, 1 Flagellate, 2 Peridineæ, and 6 Diatoms. This was 

 folio wed in 1906 by a treatise by Ostenfeld and Wesenberg- 

 Lund, "A regular fortnightly Exploration of the Plankton of the 

 two Icelandic lakes, Thingvallavatn and M\ vatn." For a whole year 

 the authors had plankton samples collected every fortnight in the 

 two lakes, having at the same time the temperature of the water 

 and atmosphere ascertained. With regard to Myvatn the result of 

 the investigation was that practically no phytoplankton was found, 

 excepting a few individuals of the genus Anabæna in one single 

 sample, but neither plankton Diatoms nor Chiorophyceæ were pre- 

 sent. (When I, in 1914, collected some plankton samples in Myvatn 

 there was a vigorous "water bloom" of^ Anabæna flos aqiiæ. Of this 

 see further under remarks regarding this species). In Thingvallavatn, 

 on the other hånd, a phytoplankton consisting of 8 species of Chioro- 

 phyceæ, 14 Diatomaceæ, 1 Flagellate, 1 Peridineæ was found, whereas 

 Cyanophyceæ were entirely lacking in the plankton. 



Among works treating of Icelandic fresh-water algae those of 

 Helgi Jonsson (1911), dealing with Rhodochorton islandiciim, and 

 E. Østrup, who gives a list comprising 468 species of Icelandic 

 fresh-water Diatoms, many of which had not hitherto been described, 

 must be recorded. Furthermore scattered remarks on fresh-water 

 algae occur in treatises by Ostenfeld (1899), Helgi Jonsson 

 (1895 I and II, 1898, 1900, 1905, 1913) and Thoroddsen (1910). 



ON THE COLLECTIONS OF CYANOPHYCEÆ MADE IN 



ICELAND. 

 The material of the present work is collected by a number of 

 difFerent travellers. An essential portion of the specimens examined 



