15 26 Proceedings of the Royal Trish Academy. 



In the low littoral region, if the F. serratus vegetation is not dense, a very 

 large number of species occur, the shelter and shade being highly suitable 

 for : — 



Dictyota dichotoma. Polysiphonia fruticulosa. 



Chylocladia ovalis. P. thuyoides. 



C. articulata. Plumaria elegans. 



Delesseria alata. Lithothamnion polymorphum. 



Nitophyllum laceratum. Sporelings, many spp. 



Comparison with other Countries. — In a general way the Fucaceae association 

 described above represents that of the whole of the British Isles. It agrees 

 well with that observed on the south and east of England, and though the 

 Fucaceae of the British Isles have never been specially investigated from the 

 present point of view, it is not likely that any startling departures from the 

 Clare Island type will be met with. The greatest variation may be expected 

 on the north of Scotland. The vegetation described for the Norwegian coast 

 is similar, agreeing floristically, but differing in minor points. With more 

 thorough investigation some of the latter will probably disappear. In west 

 Sweden, Pelvetia is absent, and Kylin makes no reference to F. spiralis on 

 exposed coasts. He notes the presence of the form F. Areschougii on moderately 

 open shores, and it would be remarkable if the short exposed form, so addicted 

 to boisterous localities elsewhere, were absent. A belt of an evesiculate 

 variety of F. resiculosus is well developed, but from specimens sent by 

 Dr. Kylin, it is clear that his form (compressus racemosus, Kjellman) is 

 different from that which occurs on Clare Island. The Faeroese Fucus 

 vegetation differs in several respects from the Irish. In the first place, 

 F. serratus is absent, F. inflatus taking its place ; F. spiralis is not found with 

 extreme shelter, and F. vesiculosus disappears entirely with exposure ; lastly, 

 Pelvetia is absent from exposed coasts. The last two points were specially 

 investigated by Dr. Borgesen during his visit to Clare Island ; and he agreed 

 that both species flourish in Ireland with very much more exposure than in 

 the Faeroes. The Fucus vegetation of Iceland is similar to that of the last- 

 named, in that it possesses a vigorous growth of F. inflatus, though F. serratus 

 is present in addition. From the brief account given by Joubin ('09), the 

 Fucaceae vegetation at Roscoff appears to agree in the main with that of 

 the British Isles. 



The Lichina communities. 



Though a lichen and not an alga, Lichina pygmaea is always found between 

 the tide-marks, and forms so essential a part of the marine vegetation that it 



