88 H. JONSSON 



If we reckon, in percentages, the number of species of each 

 group of the total number of species in the upper littoral zone we 

 obtain the following figures. The strictly littoral species (58 in all) 

 are indicated by a, the other species (20 in all) not strictly littoral 

 are indicated by b, but no attention is paid to those species which 

 may be found in the upper littoral zone and appear to grow by 

 preference in pools. 



Rhodophycea; Phaeophyceie Chlorophycese Cyanophyceae 



a 5 (9 °/o) 14 (24 %>) 33 (57 °/'o) 6 (10 %) 



a±b 18(23%) 18(23%) 36(46%) 6(8%) 



So far as the abundance of species is concerned I lay special 

 stress on the red algae, green algae and blue-green algae. It would 

 be confusing, especially as regards the red alga?, to reckon the b- 

 species as strictly littoral, nor can this be done, because they are 

 not adapted for life in the open littoral zone. As regards the brown 

 and green alga?, on the other hand, it is of no essential importance 

 whether the fc-species are included or not, as they are so few in 

 number. 



If we calculate how great a proportion the strictly littoral 

 species form of the combined number of each group we obtain the 

 following figures: — 



Rhodophycea; Phreophyceaj Chlorophycese Cyanophycese 



Species known at pre- 

 sent from Iceland.. 76 67 51 6 

 Strictly littoral species 5 (6.6%) 14 (20.9%) 33 (64.7%) 6 (100%) 

 a + b (see above) 18 (23.7 %) 18 (26.8 %) 36 (70.6 %) 6 (100 %) 



B. The Lower Littoral Zone and the Belt below down to 

 a depth of about 10 metres. 



1. The Lower Littoral Zone. From this are recorded 93 

 species in all (Table 7), viz. 39 Rhodophycece , 37 Phceophycece and 

 17 Chlorophycece. Of these 93 species, the upper and lower littoral 

 zones have 15 species in common (8 red, 5 brown, 2 green) which 

 do not extend further downwards; the greater number of these 

 belong, strictly speaking, to the lower littoral zone, as, in the upper 

 littoral zone, they usually occur in pools or very shady spots. 19 

 species (8 red, 11 brown) have been found only in the lower littoral 

 zone; but the majority of them probably occur also below the limit 

 of low-tide, and, in any case, some have their area of distribution 



