'M)'2 .ions. iu)vi; im tkuskn 



proacli f. pnnhiiiu willi wliitli llirv luivc lliis in common tliat i):irt of 

 thc mc<liuii pt)rli(»ii <•! llie valve has parallel sides. V. Heurck Syn. 

 F'l. IV. lif^. 1 I). <m tlie otiier hånd, In-ars no ieseml)lanc'e to tlie speciniens 

 of f. reiilriiusd whicli I liave seen. 'I'his form is evidenll> niiich less 

 comiiuui in Icehind than in Dennuuk. But few speciincns were found 

 in the samples menlioned. 



Navicula mutica f. producta Ciiun. Cl. und Cirun.. Arel. Dial. p. 41. 

 Van Heurck Syn. PI. X, 11^. 20a. 



Vcstmannaeyjar L. 409. 



Thc ileseri|)tion in Arcl. Dial. (1. c. shows extellenl a^reement with 

 V. Heurcks picture 1. c. whereas Cleve's deserijition Syn. I. p. 129) 

 »V. lanceolati'. with broad truncate ends« seems lo me to agree badly 

 with this form. I only tound it in few specimens in the sample men- 

 lioned ahovc. 



— — I. minima Boye V. Boye Petersen 1915, p. 287. fig. 6. 



E. Icel. L. 7, L. 4(i. L. (uS, L. 77, L. 78, L. 92. L. 112. L. 114, L. 121 — 

 N. Icel. L. 135, L. 137, L. 179, L. 184. L. 196. 217, L. 219. L. 243, 254 — 

 S. Icel. L. 381 - Vcstmannaeyjar L. 400. L. 408. L. 4(l9. 



V. Heurck's T\'pes Nr. 113 mainly contains W miiiimo in a rather 

 pointed form. A similar form often occurs in Ihe Icelandic samples . 

 As a rule formå luiiiiiud occurs in comj^any with f. (lohnii with which 

 it is connecled by forms showing a gradual transition. In a single sample, 

 however. I found f. minima alone (243). 



It may perhai)s be (piestionable whether this form should be main- 

 tained as a separate formå. but. as menlioned, it may occur in the pure 

 form, without f. Cohnii being present, and in addition growlhs of f. Cohnii 

 arc fre(|ucntly found in whicli it will be useless to search for f. minima. 

 .\ccording lo the data, ils ecology would seem to be Ihe same as that 

 of f. (.ohnii. 



— — f. quinquenodis (Grun.) N. nivalis Cl. Syn. I. p. 130; Boye Pe- 

 tersen 1915, p. 288. 



E. Icel. 7 - X. Icel. 217. 



I have only found this lorm in Iwo localilies in Iceland and very 

 few specimens of it. It is evidenlly nuich rarer in Iceland than in Den- 

 mark Boye Petersen 1. c). Ostruj) 1918, p. 11 found it in 5 samples, 

 4 of which originaled frc)m hol springs. This would seem lo indicalc 

 that it is a southern form chiefly able to thrive in Iceland by the hot 

 springs. As a matler of faet one of the samples in which I found the 

 sj)ccies was of a Ihermal nature (Nr. 217). However, liiis form is also 

 known from (ireenland and Franz Josefs land, and not from hot sjjrings. 



f. rhomboidea Playfair. Playfair 1914. p. 112. PI. IV. (ig. 7. 



Fig. nostr. 18. 



E. Icel. 112 — N. Icel. i:55, L. 184. 



