THK AERIAL ALGÆ Ol ICELAND 387 



Stauroneis parvula Grun. var. producta Grun. Cl. Svn. I. |). 149. 

 V. Heurck Syn. PI. IV, fij^. 12. 



E. Icel. 85. 



Only few specimens observed. 



Naviciila Bory. 

 Naviciilæ miniisculæ Cl. 



Navicula Atomus (Xiig.) Grun. V. Heurck, Traité des Diat. p. 227, 

 Pi. 5, fjg. 230. 



E. Iccl. L. 8, U. L. 92, L. 114. L. 121, 128, L. 131- X.Icel. L. 133, 

 L. 162, L. 173, L. 179, L. 182, 218, 219, 241. L. 252. L. 254. L. 25(5 — 

 N. W. Icel. L. 269 - W. Icel. L. 297, L. 307, L. 309 a, 321, L. 327, L. 336 — 

 S. Icel. L. 282, L. 2ii5, L. 352, L. 372, L. 373, L. 381, L. 387, 395 - Vest- 

 mannacyjar L. 409. 



Area: Eur., Jan Mayen. 



A pronounced terrestial species, as has been recogniscd already by 

 a number of investigators. e. g. Cleve, V. Heurck, and v. Schonfeldl. 

 I have previously found that this species could keep alive in soil con- 

 taining only 6,8 p. c. of water (1915 p. 7 , and by culture Miss Bristol 

 found the species (1920) in several samples of soil that had been dried 

 for up to 8 weeks. The species has thus a very considerable power of 

 withstanding desiccation. 



Already my experience from Denmark (1915, p. 290) seemed to in- 

 dicate that this species especially thrives well in rich soil containing 

 much organic matter, perhaps particularly such as abounds in nitro- 

 genous nourishment and with neutral or alkalic reaction. Miss Brist ols 

 samples of soil mostly originale from similar localities. Of the 33 samples 

 from Iceland in which I found the species, 20 were taken in the imme- 

 diate vicinity of human habitations where there is ahvays plenty of 

 manure, and probably such substances have been present in several of 

 the other localities, too. In 15 of the samples cxamined it was found 

 in Company with Prasiola crispa. Kolkwitz and Marsson (1908 p. 513) 

 class the species as /i-mesosaprobe. 



I have previously (1915. p. 21) described the extremcly hyaline 

 frustules of this species. They are most strongly silicidcd around the 

 raphe and viewed from the girdle side thej' are quite narrow. Hence 

 Miss Bristers fig. 9,io (1920) can scarcely belong to this species but 

 seems to represent a species with much more solid frustules. perhaps 

 one of the small forms of Xauiciila mutica ;?). I have also ])ointed out 

 that larger forms than those described by Van Heurck may often be 

 met with. In the Icelandic material I have found similar large forms, 

 e. g. in sample 219, in which one specimen had the dimensions: 1.13.6//, 

 br. 6,6/7, str. in the middle abt. 14, towards the ajiices abt. 23 in 10//. 

 This specimen likewise showed a dislinct transapical area. 



The species has undoubtedly very often passed unnoticed. hence it 

 is difficult at the present moment to form any opinion as lo its distri- 

 bution, but in all probability it is very widesprcad. 



