15 22 Proceedings of the Royal Irish Academy. 



The vegetation described above, taken together with the Enteromorpha 

 growth, corresponds to Borgesen's " Chlorophyceae Formation." In Clare 

 Island, the Enteromorpha vegetation is entirely distinct from Prasiola, and it 

 occurs only where certain definite conditions are present. In the Faeroes, on 

 the other hand, species of these two algal gdnera are of general occurrence, 

 and form together a well-marked green belt around the islands. The same is 

 the case in Iceland. 



Enteromorpha intestinalis Association. 



As remarked above, the Enteromorpha association of exposed coasts 

 is included by Borgesen in his Chlorophyceae formation. In Clare lsland» 

 however, the Enteromorpha growth differs so markedly from Borgesen's com- 

 munity that it is necessary to regard it as a distinct association. In the 

 Faeroes the formation is described as stretching like a green belt along the 

 coast, and composed of four associations which occur in the following 

 sequence :— Prasiola crispa, Rhizoclonium riparium, E. intestinalis, and P. 

 slipitata. In Clare Island the Enteromorpha association is quite distinct 

 from that of Prasiola, and is found, not as a continuous band, but only 

 where fresh water exudes from the cliffs. This type of green vegetation, 

 though not previously described, is frequently met with in the British Isles. 

 It is not largely developed in the Clare Island district, but is found in its 

 typical form, and is therefore included in the present account. 



On crossing from Achill Sound to the island, the association in question 

 strikes the eye as a bright green band near high-water mark, between 

 Kmnacorra and the harbour, and wherever a band of this nature is seen it is 

 a sure sign of the presence of fresh water. Where only a small amount 

 exudes, or the shore falls rapidly, the band is narrow, and a fucaceous or other 

 community follows it at once ; but with more water and a gradual slope the 

 association takes the form of wide-spreading bands which run transversely over 

 the rocks with a copious development below of Cyanophyceae and Diatoms. 

 A small amount of Rhizoclonium riparium is, on flat rocks, sometimes 

 intermixed with Enteromorpha ; but more often the growth is practically 

 pure, var. comucopiae being usually plentiful. On vertical rocks and below 

 small waterfalls Rhizoclonium is more abundant and may be dominant. The 

 forms of Enteromorpha present are mostly short forms of E. intestinalis var. 

 genuina and var. comucopiae, with the addition occasionally of var. micrococci 

 With regard to the bathymetric range of the association, its upper limit 

 varies directly with the position and manner in which the fresh water oozes 

 from the rocks. In some places the growth is completely submerged at high 

 tide, but in other spots the upper part is not even reached by the spray of an 



