92 H. JONSSON 



zone and the belt of Laminaria in the sublittoral zone. This is 

 possibly the reason why the semi-littoral zone is richest in species. 

 In Table 7 , 64 species are recorded as sublittoral. Besides 

 these, semi-littoral species occur in this zone, especially as epiphytes, 

 or, more rarely, as undergrowth. 12 species, almost all semi-littoral, 

 which extend to a greater depth than 10 metres are mentioned in 

 the table. In addition, about 14 species can be regarded as epi- 

 phytic, particularly in the upper part of the sublittoral zone. The 

 sublittoral vegetation is thus composed of 64 sublittoral species and 

 of about 26 semi-littoral species, or about 90 species in all. 



Lower Limits of Growth. 



As far as the lower limit of growth is concerned the species 

 which are found below low-tide must be dealt with collectively. 

 In the following table, which shows the lower limits of growth, all 

 the depths at which species have been known to occur have been, 

 as a rule, taken into consideration, and thus the table does not 

 indicate the depth of their general distribution or the depth at 

 which they form associations (see under Vegetation). In the table, 

 2 red algae are omitted, as I have no further knowledge regarding 

 their habitats (31, pp. 140, 141). These species are Delesseria Baerii and 

 Bonnemaisonia asparagoides. As regards the green algae it must also 

 be stated that I have not taken into consideration the records from 

 greater depths than 10 metres. I myself am responsible for some 

 of these records; the algae often were detached, but sometimes it 

 appeared as if they really had been growing at the depth recorded. 

 I always, however, have entertained some doubt concerning this, 

 and consequently prefer at present not to consider records from 

 such depths. Regarding Chlorochytrium inclusion the record is cor- 

 rect, as it grew in Turnerella, which was attached to the bottom 

 at a depth of 30 metres. For Gomontia and Ostreobium I have given 

 the most common depth, down to about 40 metres, but I have also 

 obtained these species, growing inside an old shell of Mya, from a 

 depth of about 60 metres. 



It should be further stated that I do not know the depth to 

 be given for Desmarestia ligulata. This species has been found by 

 Ove Paulsen between the Vestmannaeyjar and South-Iceland; I 

 presume that it grew at a depth of about 20 metres. 



