15 30 Proceedings of the Royal Irish Academy. 



community as a winter vegetation ; and Borgesen states that, though in the 

 Faeroes it is developed all the year round, it is in more southern countries 

 characteristic of winter. On Clare Island this is hardly the case. The 

 Porphyra association is in fine condition in July and August, and abundant even 

 on the south shore [vide Plate I). It is, however, more widely spread in winter, 

 owing partly to the presence of a band of var. linearis ; but the association in the 

 Clare Island neighbourhood certainly occurs throughout the year. Borgesen 

 also remarks that he did not observe the Porphyra vegetation at North 

 Berwick (Scotland) in July, 1909, but Dr. A. A. Lawson informs me that at 

 St. Andrews (about seventeen miles further north) it was plentiful in July 

 and August, 1910 ; though in the hot dry summer of 1911 it was much less 

 conspicuous. In the south of England it is a winter and spring vegetation, 

 though in July, 1911, the Porphyra belt was still discernible on exposed 

 rocks at Portland Bill. The exposed Porphyra association is also recorded 

 from Iceland (where it closely resembles that of the Faeroes), west Sweden 

 (Kjellmann, 78, Kylin, '07), and Norway (Kylin, '10). 



To sum up, the Porphyra vegetation of the exposed coasts of Clare Island 

 forms a belt in the littoral zone, at a very much lower level than it does on 

 the Faeroes, and does not, even in shady aud very exposed localities, grow 

 far above the high-water line. In contrast to the south of England, Sweden, 

 and Denmark, but in agreement with that described for Norway and the 

 Faeroes, it exists through the entire year. The form of the plant on 

 exposed coasts is entirely different from that found in sheltered localities. 



Bangia-Urospora-Ulothrix Association. 



The most striking feature of this community is its sporadic appearance. 

 During the first two years of the Survey scarcely a thread of Bangia or 

 Urospora was found; but during the spring of 1911 a remarkably fine and 

 widespread development of the typical Bangia-Urospora-Ulothrix association 

 occurred on Clare Island and on the exposed parts of the mainland. This 

 vegetation was probably at its best during the time of the April visit ; by 

 August it had entirely vanished. In the Faeroes it appears to be more or 

 less permanent ; but, as shown below, its sporadic appearance is known in 

 other countries, and it may even be absent for several years in succession over 

 a wide stretch of coast-line {vide Borgesen, '05, p. 720). For this reason the 

 appearance of well-marked belts of Bangia and Urospora during the last year 

 of the Survey was particularly gratifying. 



The community in question occurs on exposed and moderately exposed 

 rocks, especially where the surface is smooth and where other algae do not 

 ootain a footing. I n 1 lathymetric range the association as a whole corresponds 



