90 H. JOXSSON 



number of red algae in the lower littoral zone. This can be dis- 

 tinctly seen from the following figures: 



Upper Littoral Zone Lower Littoral Zone 



58 species (a) 93 species 



not common common not common 



51 (35.42%) 7 (4.86%) 86 (59.72% 



Upper Littoral Zone Lower Littoral Zone 



78 species (a 4- b] 93 species 



not common common not common 



54 (36.73 %) 24 (16.33 %) 69 (46.94 % 



Lower Littoral Zone From the limit of low-tide to a 



93 species depth of about 10 m. 103 species, 



not common common not common 



34 (24.82%) 59 (43.06%) 44 (32.12 % ; 



The figures show r that the upper littoral zone is very unlike 

 the lower littoral zone, especially if only the species which are 

 characteristic of the latter, or which occur in the open littoral zone 

 (a), are taken into consideration, which is most correct, as the 

 shade-loving species in the upper littoral zone must be regarded 

 as stragglers from associations lower down. As previously mentioned, 

 the lower littoral zone bears the greatest resemblance to the belt 

 which exists Iow 7 er do\vn (to a depth of about 10 metres). 



The species which have their lower limit of growth at a depth 

 of about 10 metres and which are commonly distributed in the 

 lower littoral zone I designate semi-littoral because they are found 

 both laid bare during low-tide in the lower littoral zone and con- 

 stantly submerged in the belt below r ; as these species especially 

 characterize the lower littoral zone and the belt below to a depth of 

 about 10 metres I designate this area the semi-littoral zone. It must 

 not be concluded, however, that semi-littoral vegetation covers the 

 bottom everywhere down to a depth of 10 metres; below the limit 

 of low r -tide the semi-littoral vegetation appears rather to consist of 

 stragglers from the lower littoral zone into the Laminaria-be\i. Thus 

 the semi-littoral zone is situated between the Facus-belt and the La- 

 in inar za-belt. The species which specially occur in the semi-littoral 

 zone I designate on the whole as semi- littoral, also those which are 

 found in the lower littoral zone and are not found below the limit of 

 low-tide; they will probably be found also below this limit. Species 

 which are common in the lower littoral zone and are rare in the 



