110 Scientific Proceedings, Royal Dublin Society. 



plateau at Old Boat-liouse, and at other places, there are numerous small 

 shallow rock-pools of this nature, which ai-e often dry in summer, but in 

 winter are filled by spray and rain. On the sides of the deeper pools, A. 

 halodytes is sometimes seen as a narrow band below V. mauva, and is here 

 often associated with the orustaceous red alga Hildenbrandtia protott/pus, and 

 the bottoms of the shallower hollows are also frequently coated with a crust 

 of these two species. These situations are similar to those which Weddell 

 describes as the usual habitat of A. halodytes on the coast of France. 



At various places round the coast fresh water flows over the rocks. At 

 Eed Eocks and White Water Brook small rills enter the sea, at other places 

 small springs occur on the top of the cliffs which overflow and moisten the 

 surface or drop on the shore below and spread over the rocks when the tide 

 is out. Two or three of these small waterfalls occur on the north coast 

 between Balscadden Bay and the Nose. At other parts surface drainage, 

 which is considerable in winter, runs down the grooves and cracks on the 

 cliff-faces, and on the Broad Strand large tracts of rock on the beach are kept 

 constantly damp by fresh water oozing from the base of the cliffs. These areas 

 are often easily recognized by the presence of the gi'een seaweed Enteromorpha 

 intestinalis. In situations such as the above-mentioned the continuity of 

 the V. maura belt is broken and another dark encrusting vegetation appears, 

 which is composed mainly of colonies of V. aquatilis. On tlie wet cliH-faces 

 these growths are seen as dark streaks, and extend riglit up to the top in 

 many places. Where the supply of fresh water is scanty, V. aquatilk does 

 not descend below the V. maura belt ; but where the flow is constant and fairly 

 plentiful it covers much larger areas and is found as far down the shore as 

 the influence of the fresh water lasts. On the south shore of Balscadden Bay 

 V. aquatilis forms black patches here and there on the moist cliff-faces 

 growing in the upper part with the moss Weisaia verficillata, and lower 

 with Enteromorpha intestinalis, which begins a few feet above high spring- 

 tide mark, and accompanies V. aquatilis throughout the Pelvetia zone 

 down the shore, well into the Fucus spiralis belt. 



On the damp shaly rooks lying above high-water mark on tlie Broad Strand 

 a similar, but much sparser, growth of V. aquatilis occurs. Arthopyrenia 

 halodytes is here associated with V. aquatilis on some of the rocks, and on others 

 it covers the surface with a warm brown stain of pure growth. A. leptotera is 

 also frequent. This last species does not, however, extend up the beach as 

 far as A. halodytes, but is confined to crevices and to the moister parts of the 

 rock-surface. 



On the Harbour walls, where there is a more or less constant supply of 

 fresh water from surface drainage, V. aquatilis forms a thin interrupted 



