374 JOHS. BOYE PETKRSKN 



Tilis r;ircly obsiTvcd varicly \\;is roiiml l)\ ().slriii) in 1 siiiuple 

 from frcsh \v;iter. Liko Ur- other vaiicties ol' lliis s|)ccics it is liardly 

 nii ai-rial form. 



Fragilaria construens vai. binodis dnin. V. 11 Tiailc p. 32(). i'l. 11, 

 lig. 4.Vi 



N hel. L. 1()9. 



O s I ni |) li sam|)les. 



var. venter C.nin. V. H. Traitc- j). 325, PI 11. lig. 451. 



X. kel. 252. 

 Østrup 53 samples. 



— — vai- genuina ('■riiii. Mcisler l'J12 p. 07 Tab. \T. lig. 6. 

 N. Icel. L. Ki'J. 



Ost ru p 52 samples. 



Fragilaria lævissima Cleve. ('-1.1898, p. 9. Bove Petersen 1924 II. 

 p.318, lig. 7. 



E. Icel. 99, 128 X. Icel. L. 179, 252 — W. Icel. 336 — S. Icel. L.V327. 

 Area: Jan Maven, Fr. Jos., Murray Isl., Walrus Isl., X. Greenl. 



Tilis species which has only heen observed a few times, is pre- 

 sumably of northern distribution. It occurs in (|uantity in several ol" 

 the samples mentioned above, thus in sample 179, which was collectcd 

 on the ground in a lava cave whcre shee]) had sheltered in bad weather, 

 anil whcre tliere was conseciuently soine nianure on the ground. It seenis 

 especially to tlirive well on rocks with dripping water. Xot previously 

 found in Iceland. Probably an aerial species. 



Fragilarla mutabilis C.run. Meister 1912. ji. (iS, Tab. VI. lig. 14. 

 H. Icel. 85. 99. 128 — X. Icel. Kil. 



Three of the above-menlioned samples are derived from rocks with 

 trickling water, so presumably the species is not uncomnion in such 

 iocalitit's. However. il appears to be conimoner in fresh water since 

 Østruj) has found it in 39 samples from such localilies. 



Fragilaria virescens Halfs. Meister 1912 p. 66, Tab. V, lig. 26. 



K. Icel. 113. 123 — X. Icel. L. 1()9, 256 — W. Icel. 321, 327. 336, 

 338 - S. Icel. 295. 



Ost ru p has it IVoiii 30 samjiles from fresh water. In most of the 

 above-mcntioned samples I found only a few specimens of the species. 

 I only found it in greater (juantity in sam])les 169 and 256, bolh ori- 

 ginating from piaces where there is jilenty of water, at any rate at times. 

 Will hardlv withstaiid anv verv intense desiccation. 



