86 Scientific Proceedings, Royal Dublin Society. 



with the surface of the sea at a few feet below the level of ordinary high tide, 

 contrasting in a striking manner with the paler band of the barnaole-covered 

 rock below it. These two bands, the dark lichen band and the paler barnacle- 

 covered area, are to be seen on all the cliffs round the headlands, the dark 

 band rising higher on the parts wliich stand more out to sea; but they are 

 most conspicuous on the steep cliffs rising out of the deep water on the 

 eastern coast, on which, at low spring-tide, yet another dark baud composed 

 of algae (Fuci and Laminaria) can be distinguished below the barnacles. 

 This dark lichen-band is wider on sloping surfaces and on flat shores, and is 

 most intense in colour a little above and below high neap-tide level, shading 

 off upwards and ending in a ragged uneven outline. On the rocks of the 

 Broad Strand and other low shores, these dark lichen-growths stretch from 

 the highest spring-tide mark to the lowest spring-tide mark, on the upper 

 part of the shore forming a continuous sheet of vegetation which is most 

 conspicuous above the ordinary high-tide mark, where it is unobscured Jby 

 algae, but tailing off and becoming patchy as low-water mark is approached. 

 The upper part of this dark lichen-band is occupied by the Verrucaria maura 

 belt referred to by Warming. Below Verrucaria maura another belt occurs 

 not mentioned by Warming — the belt of marine Yerrucarias. Besides these 

 there are two other belts or zones which form elements of the dark lichen-band, 

 those of the shrubby Lichinas, L. confinis and L. pijgmaea. The former of 

 these grows along tlie upper, and the latter along the lower limits of the 

 Verrucaria maura belt. Above the dark band the orange belt of Placodium 

 muroritm, Physcia parietina, &c., stands out conspicuously, and above the 

 orange belt the grey-green growtlis of the Ramalinas occupy a wide area_ 

 These three colour-belts occur all round the coast, and can be well seen by 

 standing on the shore just below high neap-tide level and looking towards 

 the cliffs. On the beach at Stella Maris they occur with beautiful regularity. 

 The Ramalina belt would correspond to Weddell's maritime group ; the main 

 part of the orange belt and the Verrucaria maura belt would be included 

 in his semi-marine group ; while those species growing below high neap- 

 tide level would constitute his marine group. As, however, the arrangement 

 in belts, which might perhaps be described as linear associations, seems to be 

 the natural way in which the lichens of the sea-shore group themselves, I 

 have decided to adopt it rather tlian Weddelrfe classification in describing 

 the lichen-vegetation of the Howth coasts. 



In many places the lichen-belts exhibit a further subdivision into zones 

 which vary somewhat according to the lie of the shore and the amount of 

 exposure, &c., but these variations will be dealt with when describing each 

 belt in detail. 



