THE AÉRIAL ALGÆ OF ICELAND 403 



Pinnularia Brebissonii Kiitz. Cl. Svn. II, p. 78. Van Heurck Svn. 

 PI. V, fig. 7. 



E. Icel. 75. 129. 



Lagerstedt already observed this species on earth and nioss in 

 Spitzbergen, just as I niyself have found it on earth in Denmark. In 

 Iceland, however, it seems predominantly acpiatic Østrup 34 samples). 

 Both the samples in which 1 found it were derived from damp rocks. 



Pinnularia Gandrupii Boye P. Boye Petersen 1924 III, p. 16, fig. 4. 

 E. Icel. 8 — N. Icel. 218. 



This form, which I have previously found in samples from Jan 

 Mayen, only occurred in a few specimens in the above-mentioned samples. 

 It is questionable whether it is an aerial s])écies. It is very reminiscent 

 of the forms I have referred lo P. appeiidicuhita var. irrnrata, and might 

 perhaps be regarded as a variety of this species. 



Pinnularia gracillima Greg. Cl. Syn. II, p. 74. Van Heurck Svn. 

 PI. VI, fig. 24. 



E. Icel. 8, L. 25, 77, 78, 85. 92, 99, L. 124, L. 128, L. 129 - N. Icel. 

 140, 169, 179 — W. Icel. 336 — S. Icel. 353, 372. 



The species has hitherto only been known from fresh water. Østrup 

 found it in 6 samples from fresh water in Iceland. I have observed it 

 with cell contents in 4 samples (25, 124, 128, 129) all originating from 

 rocks, 3 of which were overgrown with moss. Thus it is certain that 

 it can live terrestrially. In the other samples I have onlj"^ seen com- 

 parativelj' few specimens and none with cell contents. Several of thcse 

 samples were from the immediate vicinity of houses where there is al- 

 ways plenty of manure. The species would thus secm well able to thrive 

 under such conditions, whereas it does not seem to require any great 

 quantity of nitrogenous nourishment. 



var. interrupta Fontell. Fonteli 1916, p. 33, PI. 2, fig. 45. 



P. gracillima Hustedt 1914, p. 74, Taf. II, fig. 43. 



E.Icel. 7, 24, 78, 99, 129 — N. Icel. 215, 2l7. 



This variety occurs in several samples in company with the typical 

 P. gracillima (78, 79, 129i, and should perhaps most correctly be regarded 

 as a formå, experience having shown that many species occur in the 

 genus Pinnularia both with and without transapical fascia. It is very 

 reminiscent of P. nndulala but dillers from the latter by its rostrate, 

 not capitate, apices. (Cf. Hustedt 1. c). It seems chielly to occur in 

 the same piaces as the main species. 



Pinnularia Intermedia Lagcr.st. Lagerstedt 1873, p. 23. T. I, fig. 3. 

 Bove Petersen 1915, p. 293. fig. 18. 19. Bristol 1920, p. 66, fig. 6-9. 

 A. S. Atl. T. 313, fig. 28. (non Hustedt 1924, p. 569, Taf. 21, fig. 10,. 



