THE AKRIAL ALGÆ OF ICELANO 397 



This species which I have previously found on tlie gruiind in Den- 

 mark is evidently neaiiy allied to A'. pseudohacilliim Grun., showing 

 especially great correspondence with V. Heurck Syn. PI. 13, (ig. 13. The 

 systeniatic place of Ihis form has been somcwhat dubious (Cl. Syn. I, 

 p. I37f.). On measuring the flgiire Ihe foHowing ligures result: L. 27^/, 

 hr. 1 ju, str. 18 in 10 /< in the middle, which is in fairly close agreement 

 with N. terreslris which, fiirthcrmorc, has. in faet, valves that are some- 

 what gibbons in the middle, though this does not api)car in the ligure 

 (1. c.) (Judging by the dimensions and description it is not impossible 

 that N. terricola Bristol (1920 p. 67, fig. 15— 17) is in reality the same 

 species). Only found on earth, in Denmark especially field and garden 

 soil, in Iceland on pure mineral ground. 



Naviculæ decipientes Cl. 



Navicula subtilissima Cleve Cl. Syn. I, p. 141. Stauroneis linearis 

 Lagerst. 1873 p. 37, PI. II, fig. 13. 



N. Icel. 217. 



Only few specimens observed in the sample. They bore a close 

 resemblance to the flgure of Lagerstedt cited, but did nol resemble 

 Cleve's figure so closely. (1891, j). 37, PI. II, fig. 15'. The dimensions 

 were somewhat smaller than stated by both authors, viz. L. 17/^ br. 5,5//. 



Naviculæ heterostichæ Cl. 



Navicula cocconeiformis Greg. Cl. Syn. II, p. 9. V. Heurck Syn. 

 PI. 14, fig. 1. 



E. Icel. 125, L. 128, 129 — N. Icel. 217, 256. 



According to Cleve, an arctic-alpine species, oflen found in water, 

 thus by Østrup in 13 samples from Iceland. It evidently belongs to 

 the species that thrive well both in water and in damp piaces on land, 

 e. g. among mosses and on irrorated rocks. 



Naviculæ punctatæ Cl. 



Navicula pusilla W. Sm. CI. Syn. II. p. 41. Van Heurck Syn. PI. 11, 

 fig. 17. 



E. Icel. 40 — Vestmannaeyjar L. 403, L. 408, 409, L. 410. 



Stated to occur in fresh water as well as in slightly brackish water 

 (Cl. 1. c). It is, however, already mentioned by Pfitzer aftcr Deby 1879) 

 as a terrestrial species, and later it was found by Deflandre (1926) 

 on damp rocks in Xormandy. In Iceland, however, it evidently occurs 

 chiefly in fresh water (Østrup 40 Pr.). 



Naviculæ orthostichæ Cl. 



Navicula gregaria Donk. Cl. Syn. I, p. 108. Van Heurck Syn. PI. VIII, 

 figs. 12—15. 



Vestmannaeyjar L. 410. 



