'MMJ .ions. HOii: l'KTKHSKN 



In llu' nhovt'-nu'iilioncd ravine -Shua (ij;! nt'ar M\\aln(.see p. 803) 

 at the bolloni ol" whicii thcre was a hol sprini^ itcnip. ahl. 'iS") there 

 was an ahundant algal vegetation on the earlli and niud, eonsisting 

 ol' Oscillaloria leniiis and Diatonis in (pianlily, Ihe coninionest being 

 Achnanlhes lanceohita. Sanicnla cnjjitocephula v. nencla, \. Ihenuicola, 

 Pinniilarui mesolepla n. slduronei/ormis, an(i P. subaipUatd (215, 218). 

 ( )n Ihi- ground on tlie hank ol" a stieani issuing from rxahver 

 (\. Iceland 241) with walcr at a temperature ol .")-t" I found (Ajlindro- 

 spermnm iiuiscicola togelher wilh a nuniher ol' Dialonis (see Boye 

 Petersen 1928 p. 802). Hound a small »hver« (boiling spring) at 

 Laugarvatn (8(U) there was a growth ol" Schizoihri.v Friesii on the 

 gioiind, hesides 4 species ol' Diatoms ol" which Caloncis fasciata was 

 Ihe commonest. 



At Uxahver (N. Iceland) I have seen how a true thermal alga 

 will grow on the siliceoiis sinter above the surlace ol" Ihe water. 

 The water ol" the spring was so hot (near 100*^) that algæ could not 

 grow in it, but on the siliceous sinter above the surface there was 

 a handsome helt ol' Hapctlosiphon laminosns f. tijpica (237). I have 

 j)reviously given a detailed description ol" tiie hot spring at Klepp- 

 jarnsreykir (1928, p. 280) where Phormidiiim Treleasei as well as 

 Sliffoncma panniforme grew in a similar way on the siliceous sinter 

 (815. 816, 817, 818). The latter species also grew at Deildartungahver 

 (888), whiie Calothrix thermalis occurred at Sturlureykir (880) under 

 almost identical conditions. As a rule Diatoms do not occur on 

 the sinter around the springs. An exception occurred at the hot 

 spring near Helgavatn (887) where Sipni)loca Miiscoriim occurred 

 (Boye Petersen 1924, p. 28()) together with 6 species ol" Diatoms, 

 the connnonest being Rhupalodia gibberiila. As will appear from 

 the list ol" them in the summary ol" the samples examined, these 

 species are not especially thermophilous but are usually found on 

 damp ground or rocks. 



An abundant llora of algie consisting of Cyanophyccæ, Chloro- 

 [)hyceæ and Diatoms is also very ol'ten found in the luxurianl lufts 

 of moss growing round the hot springs (Hesselbo 1918, ligs. 21 — 

 28). ir the water from a tult of moss is squeezcd into a glass, a 

 great (juantity of these dilTerent algæ will fre(|uenlly appear. Thus, 

 ol Cyanophyceæ I have found Schizoihri.v Miilleri (Reykholl 822) 

 (Boye Petersen 1928, p. 290). The Chlorophyceæ are especially re- 

 presented by several species of Desmidiaceæ (828, 331, 884). The 

 Diatoms, however, are mosl abundantly represented. I shall not 



