THE AERIAL ALGÆ OF ICELAND 373 



Tetracijcliis Halls. 



Tetracyclus lacustris Halfs var. emarginata Ehr.) W. Sm. Van Hciirck 

 Traité p. .'558. 



N. Icel. 256. 



Only a single specinien observed. Tcti-aci/clus Bnninii i.s a comnion 

 species on damp rocks in Europe, and thc present form maj' possibly 

 occur in a similar way. I found it on a mountain slope near Siglufjorciur 



Denticula Kiilz. 



Denticula frigida Kiitz. Meister 1912 p. 59, Tab. 5, flgs. 5-6. 



E. Icel. L. 25, 129. 

 Area: Eur. 



This species is closely allicd to D. tenuis Kiitz. and is as a rule, and 

 perhaps rightly, not distingiiished from that species. According to Meister 

 it occurs chiefly in cold water, both running and stagnant. In sample 25, 

 originating from moss in a mountain cleft through which watcr from 

 the melting snow would no doubt trickle in the spring, I found specimens 

 with cell contents. In the other sample, from a rocky wall, it occurred 

 among various Cyanophyceæ, amongst others Desmonema Wrangelii, gene- 

 rally found, too, in cold mountain streams. It must then be supposed 

 that, at any rate in the spring, cold water trickles down this rocky 

 wall. The two localities thus agree well with Meister's statements. 

 The species will then presumably grow up in all the little streams running 

 down the mountain sides in the spring, and when these run dry in the 

 course of the summer, it will probably survive for a little while, but 

 later in the summer most of Ihe specimens will presumably die, except 

 a few that will survive and reproduce themselves next spring. Hence 

 the species must probably be classed among those that form a transition 

 to the terrestrial Diatoms. 



III. Fragilarieæ. 



Fragilaria G run. 



Fragilaria capucina Desm. Meister 1912, p. 66. Tab. VI, fig. 2. 



S. Icel. L. 386. 



Østrup only found it in 2 samples from Iceland, so it does not 

 seem to be common in the island. The locality in which I found it 

 was very damp, so it would hardly be warrantable to conclude from 

 this occurrence that it may appear as an aerial alga. 



Fragilaria construens (Ehr.) Grun. var. pusilla Grun. Meister 1912 

 p. 67, Tab. VI, fig. 8. 



E. Icel. 128. 



The Botany of Icelnncl. Vol. II. 25 



