370 .ions, novK pktfrskn 



Iii lUe succiHnliiii* j)arl, I have ns a lule, uiuk-r Ihr iii(ii\ idiial 

 species, stated in how niany samples from IVesh water Østru|) 

 foiuul tlie s|)eeies in Iceland (Øsliii|) 1918). A eompaiison of lliesi- 

 figures with Ihe number ol" samples in wliich I have loinid Ihe 

 species will Inrnish an ap|)io\imate nnmerical basis from which 

 wi" oan lind out whelher Ihe species is chielly lent'strial or ;u|ualic. 

 It shonld be noted, however, that since Østrup has examined abl. 

 ;■)()() samples IVom Iresh water, while I have examined abl. 100 from 

 land. Øst ru !> s lignies shonld i)e divided by o before comparing. 



CENTRICÆ. 



Melosira crenulata Khrb. Kiitz. van Goor 1924. p.'.VM. 



E. kel. 4. 7. 24. 77. 113 — X. Icel. L. 1G9, 256 - \V. Icel. 321 - 

 S. Icel. 295, 372. 



I takc tilis species here within the same limits as van Goor 1. c. 

 The majority of the forms I have found correspond to M. itctUca, only 

 in one sample did I lind frustules oi M. creiiulttla scnsu O. Muller 1904. 

 p. 2()4 . It is a i^cculiar faet that only short cclls have bccn ohscrvcd 

 in the tcrrcstrial sam|)les. As regards the thickness of the lilaments, the 

 speciraens found corresponded to M. crenulata, M. ilalica, M. italica tennis, 

 and M. italica tennissinia. Only in one sample were living cells ascertained 

 with certainty. in the rest all cclls seemed to hc dead. N'everthelcss I 

 include the s|)ecies hcrc for the sake of compleleness, since the frustules 

 occur in several samples, and since I hclievc that a few specimens might 

 perhaps he able to survive in the earth and reproduce themselves, should 

 favourahle conditions again occur. even though the majority of indivi- 

 duals die away in periods of desiccalion. Tlu' species is of connnon 

 occurrence and prohahly lives chielly in the plankton of lakes and ponds. 

 whence il |)asses into the nuid of the hottom, while nunierous other 

 specimens are washed up on to the hanks. Hencc we may e\i)cct lo 

 lind it on areas near the shores of lakes which are lloodcd at cerlain 

 seasons, and it is presumahly from such localities thai il is oflen hroughl 

 by human agency f)n to the land surrounding human dwcllings, e. g. in 

 turf dug up in damp phices. The localilies in which I have found the 

 species in Iceland fall inlo two groups: 1 Very damj) i)lnces near the 

 shores of lakes or streams, and 2) farms and their iinnu-diate neigh- 

 hourhood fhladi. Øslruj) has Ihe species from much more llian a 

 hundred localities. It is diiruull to sav just how many, since he slates 

 the nund)cr of .samples for Ihe individual fornis. while it is irnjjossihle 

 to scc wiicther or not several forms occur in the same sample. This 

 shows Ihal Ihe species is hydrophilous and is only exceplionally found 

 on land where il can hardiv live long. 



•n- 



