4H) joiis. iu)vi: i>i:ii:hsi:n 



Nitzschia communis Habenhorst. CA. cl (iiiuiow, Arcl. Dial. j). 1)7. 

 Van Ileuirk Syn IM. 09. lig, :\2. 



K. Icel. 2'). 28, 99 - N. Icel. 217 - S. Icel. 386. 



Ostiu]) (locs nol mcntion lliis .species. I have not hccn ablc to 

 find s|)eciniens with cell coiitcnts in any of Ihe samples wliicii all orij^in- 

 atcd from piacos willi a fair aniouiil of moislure. Honcc tlie species 

 will not, probahly, witlisland niiicli desiccation. 



var. abbreviata nrun Cl et Gnin. Arct. Dial i).y7. Van lleiirck 



Syn. PI. 69, lij<. 'Ao. 



K. Icel. 7, 28, 121 - X, Icel. L. \:VA, L. 137, 217. L. 218 - \V. Icel. 

 L. 307, L. 337 — S. Icel. 3o2. 



1 have previously observed Ihis shoii variety of A'. communis on 

 earth in Denmark. In Iceland it has nol been observed before. bul 

 seems lo be fairly comnion on earth. It was fre(|uent in samples 133 

 and 137. In several of the localities inentioned therc \vas plenty of 

 manure 28. 133, 307. 



Nitzschia debilis Arnolti Grun. Van Heurck, Traité, p. 385, PI. 15, 

 fig. 497. 



E. Icel. 7, L. 25. 128 — N. Icel. 217, 218, L. 253 — Vestmannaeyjar 

 L. 399, 410. 



1 have previously found Ihis sjjecies in Denmark on earth of various 

 kinds. In Iceland Østrup only found it in one sample from fresh water, 

 hence it must be assumed to be a true acrial species. Judging from 

 the occurrcnccs hei"C observed it would seem to Ihrive hest on a purely 

 mineral ground. It is only in sam|)le 410 (bird-clilV thai large amounts 

 of nilrogenous organic substances may be supposed to have been present. 



Nitzschia Denticula Grun, Cl. und Grun. Arct. Dial. ji. 82. Van II. 

 Syn. l'l. 60. lig. 10. 



K. Icel. L. 7, L. 85 — N. Icel. 217 - W. Icel. 338. 



The species, \vhich was found by Ost ru p in 28 samj^les from fresh 

 water. evidently only occurs occasionally on land where, however. it 

 will thrive well when it is not loo dry. Il does not seem lo re(|uire 

 much organic matler in the substratum. 



Nitzschia dissipata Kutz.' Grun. Cl. und Grun. Arcl. Dial. p. 90. 

 Van Ileurck, .Syn. PI. 63, lig. 3. 

 K. Icel. 7. 



A few specimens were found in the sam])le of a Xitzschia with almosl 

 central carina and the following dimensions: L. 24//, br. 3,6 // , carinal 

 duts abl. 10 in 10//. slriæ very fine. I lake these lo belong to X. dis- 

 sifHilu Ihough the dimensions do nol (|uitc agree with Ihosc given by 

 (Heve and Grunow (1. c). The s|)ecies has ])reviously been found on 

 damp rocks and in similar localities (v. Schon fel il t 1913), also in a 

 rocky cave (Hu stedt 1922, p. 100. 



