108 Scientific Proceedings, Royal Dublin Society. 



submerged later tlian Pelvetia by the incoming tide. The belt is nowhere a 

 wide one on the Howth coasts, and is always more restricted in area on steep 

 shores in sheltered localities. Oa the steep cliffs it is often only a couple of 

 feet wide ; but it covers a greater extent on the low shore of Broad Strand, 

 at Stella Maris, measuring more tlian a couple of yards in places. The limits 

 are always well defined in sheltered localities, but where the coast is much 

 broken, and there is spray, V. maura grows at higher levels, and the outlines 

 of the belt are very irregular, the growth in the upper part being scattered, and 

 rising on the rocks as far as the spray reaches. On Drumleck Point, and at 

 various other places on the south-west coast, V. maura is found in spots and 

 streaks among the Ramallnas. But nowliere, even in the most exposed parts 

 of the coast, does V. maura cover the cliff-faces with a continuous crust more 

 than 8-10 feet wide. 



The belt is most conspicuous and best developed between Red Books and 

 Baily on the south-west and south coasts. Along the Sutton Creek from Old 

 Quay to Red Rocks the shores are very flat, with a few low rocks lying above 

 ordinary high tide-mark. The bottom of the sea is sandy, and the constant 

 scour of the sand-charged water over the rocks prevents the growth of 

 crustaceous lichens. V. maura is here found only in small patches in hollows 

 and cracks about high spring-tide level. At the Martello Tower, however, 

 where the rocks stand liigher, a great part of the surface is closely covered 

 with a good growth of tlie lichen. Between these liigh rocks and Red Rocks 

 the foreshore is composed of strewn rocks and boulders on a sandy bottom, 

 and all crustaceous lichen growths are conspicuously absent from the rocks 

 between tide-marks. Along the Broad Strand V. maura grows abundantly. 

 In some places the rocks are so uneven that it is difficult to see the limits 

 of the belt, but, on the boulders lying above Pelvetia at Stella Maris, where 

 the shore sweeps round towards Lion's Head, these are beautifully defined. 

 On the steeper east coast the belt is narrow, and lies mainly between tlie two 

 Lichinas, which form two well-marked bands, L. conflnis above and L.pygmaea 

 below it on the rocks. 



Verrucaria maura is the dominant lichen in the belt, but others, V- 

 memnonia, V. prominula, and V. aquatilis, contribute to its formation, and are 

 characteristic of certain situations. V. scotina also occurs occasionally. 

 Besides these a number of other lichens, invaders from the belts above 

 and below, are often found. Arthopi/reuia halodytes, A. leptoiera, and 

 A. halizoa are some of the most frequent from the lower belt, but they 

 are not able to endure the same amount of exposure to sunlight and air as 

 V. maura, and do not grow in the open at these levels, but always occur in 

 shade, or in cracks and crevices, where they find conditions most nearly 



