THE AERIAL ALGÆ OF TCELAND 



399 



Navicula cpyptocephala Kiitz. var. angusta Boye P. n. var. 

 Valva lineari-lanceolata, subrostrata, apicibu.s rolundatis; 

 long. 18/<, lat. 3,7//, striis 18 in 10//. Fig. 21. 



E. Icel. 7, 124 — N. Icel. 1(59, L. 217 — S. Icel. L. 386. 



DifTers from thc other varielies of thc species especially 

 by its narrow form and its comparalively broad apiccs. Only 

 found in piaces with jilenty of moisture, it does not pro- 

 bably withstand desiccation very well. 



var. exilis Kutz. Cl. Syn. II, 



Syn. PI. VIII, lig. 2, 4. 



N. Icel. 169 - S. Tccl. L. 386. 



p. 1 4. Van Heurck 



Fig. 21. 



\(iviciil(t 

 cnifilove- 



phaUi Kutz. 



var. aiujusta 



n. viir. 



(X 1200). 



Østrup found this variely in 25 samples from fresh watcr, and it is 

 probably no aérial form. Bolh my samples are from very damp localities. 



var. veneta Kiitz. Cl. Syn. II, p. 14, Van Heurck Syn. PI. VIII, fig. 3. 



N.Icel. L. 215, L. 217, L. 218. 



I have found this form in Denmark living on garden soil and mea- 

 dows. The 3 samples from Iceland in which I found the s])ecies are 

 all from Stora Gja, the remarkable basalt cleft east of Myvatn, which is 

 always damp because a hot spring flows out into the botfom of the 

 cleft. Østrup has not menlioned this variety as occurring in Iceland. 



Navicula Falaisiensis Grun. var. lanceola Grun. Cl. Syn. II, p. 21. 

 Van Heurck Syn. PI. 1 4, fig. 6 b. Van Heurck Types No. 127. 



E. Icel. 125. 



I have i)reviously found N. Falaisiensis on carth in Denmark. As 

 it belongs on the whole to the less frequent species, and has not been 

 found in Iceland before, it is possible that it is really an aérial species. 



Navicula Gastrum Ehrb.var. exiguaGreg. Cl. Svn. II, p. 23. Van Heurck 

 Syn. PI. VIII, fig. 32. 



N. Icel. 218. 



I have previously found this variety on arable land in Denmark 

 (Boye Petersen 1915, p. 292). Østrup found it in 10 samples from 

 Iceland, so probably it is hydrophilous. 



Navicula peregrina Ehrb. var. Meniscus Schum. Cl. Syn, II, p. 18. 

 Van Heurck Syn. PI. VIII, fig. 19. 



Vestmannaeyjar L. 399, L. 401. 



According to Cleve this is a brackish water species, but it may 

 evidently also occur in quite fresh watcr. On the Vestmannaeyjar I 

 found it in caves in a rocky wall at a height of abt. 20 m above the 

 sea. It cannot be considercd ([uite precluded that it may be dashed 

 with foam and spray from the sea in stormy weather. 



