410 JOHS. HOYK PKTKRSKN 



P. i'iridis var. coininnUiUi is uiulouljlcdly most wiilcsprcad in Iresli 

 watcr vOslrii]) 148 samples!. Ncvcrllielcss it not infrc(|iK'nlly occiirs 

 on land. and in 5 sani|)k's I foiind sj)ecimcns willi ccll contents. In 

 most cases I foiind il amon^ niosses on rocics or on piirely mineral 

 f^roiind. but also in a lew cases near houses sani|)les Kl, 92, 29S). 

 Probably il is among liic lorms Ihal cannot llirive on soil containing 

 much organic subslance. In Ihis connection I may menlion liial Kolk- 

 wilz and Marsson (190(1. p. 517 regard P. viridis as oligosaprobe. 



Pinnularia viridis Nitzsch v. rupestris Ilanlzscli. Cl. Svn. 11, p. 92. 

 A. S. All. Taf. 45, lig. 38-44. 



W. Iccl. 338. 



In llie specimcns l'ound the ajiical area scemed somewhal broader 

 than lypical of Ibis form. Found in a sample from a polalo Meld 

 near Ibe bol springs al Helgavaln, among Vaiicheria. 



VII. Gomphonemeæ. 



Gomphonemci Ag. 



Gomphonema acuminatum Hbrb. f coponata Ebrb. Cl. Syn. I. p. 184. 

 G. acuniinatuni V. II. Syn. PI. 23, iig. 16. 



X Icel. L. 169. 



The sample in wbicb Ibis l'orm was found originales from a very 

 damj) locality. Il is bardly an aerial alga. 



Gomphonema angustatum Kiitz. var. productum Grun. Cl. Syn. I, p. 181. 

 Van lleurcU. Syn. PI. 24, fig. 52 — 55. 



K. Icel. 8, 41. 77. 78, 112, L.V 113, 123, 125 - X. Iccl. 162. 173 — 

 W. Iccl. 297, 336 — S. Iccl. 295. 



.\s Nvill appear from Ibe abovc list of localities. Ibis variety was 

 found in 13 samples; liowever, it was not possible to ascerlain tbe 

 pre.sencc of individuals witli ccll contents. Since tbcre wcre also only 

 few specimcns in eacb sample, and since it is common in fiesl) watcr 

 (Østrup 87 samples, il is not probabic tbal it is i)articularly well 

 suiled for an aerial life. 



Gomphonema gracile Hbrb. var. dichotomum W.Sm. Cl. Cl. Syn. I, 

 p.l82. Van Ikiirck Syn. PI. 24. lig. 19. 



i-:. Iccl. L. 15. 



Tbis otbcrwise very widesjircad and common form is evidently not 

 very common in Iceland Ostrup 4 samples. In Ibe sample I found 

 it living among Pnisiohi on a wall. 



Gomphonema intricatum Kiitz. Cl. Syn. I. |). 1 81. V. II. Syn. P1.24,ng.28. 

 N. Icel. 256. 



