112 Scientific Proceedings, Royal Dublin Society. 



are nowhere plentiful ; Arthopijrenia foveolata and A. Kloralis are common 

 on barnacles, but as the two last-mentioned species do not seem to grow on 

 the silioious rocks, they are not included as elements of the belt as developed 

 on these coasts; their distribution is given in connexion with the marine 

 lichens of the limestone area. 



The composition of the belt varies chiefly with the nature of the rock- 

 surface. On smooth rocks Verrucaria mucosa is the prevailing species, while 

 V. tnicrospora seems to be more abundant on the rough quartzites and grits. 

 Both species are very common round the coasts, and have a wide vertical 

 range, extending on the south coast from the Pelvetia zone down to the 

 lowest ebb-tide mark ; but the main part of their growth lies in the Fncus 

 spiralis belt. 



Verrucaria microspora seems to be better able to accommodate itself to a 

 variety of conditions than V. mucosa, as it grows on botli rough and smooth 

 surfaces, and on hard and soft rocks. Its vertical distribution also seems to 

 be slightly greater ; it is more often found at Pelvetia level, and also is the 

 more usual of the two species on the rocks inside the Laminaria belt. When 

 growing on the soft shales, the thallus of V. microspora is almost evanescent, 

 and the perithecia are somewhat larger than usual. Along its upper and 

 lower limits it also varies. In its lowest limits V. microspora is exposed to 

 the air for only a very short time each day during spring-tides, and can 

 receive only very little fresh water, while at neap-tide it is completely 

 submerged for days at a time. The spores of specimens from low spring- 

 tide level were mainly abortive ; but one or two fertile spores were found, 

 which were slightly longer and narrower than normal, but otherwise 

 characteristic. Considering that both V. microspora and V. mucosa are able 

 to live submerged for long periods, it is rather curious that neither species was 

 seen in any of the small rock-pools in the upper part of the shore. Amongst 

 the Pelvetias, V. microspora var. mucosula, in which the perithecia are smaller 

 and more numerous and the spores rounder than in the species, occurs. It is 

 frequent on the Broad Strand and at several other places on the south coast. 

 This variety seems always to grow at a higher level than V. microspora, and 

 is often associated with Arthopyrenia halodytes and with Verrucaria striatula, 

 f. continua, which is very common on the Howth shores. V- striatula 

 i. continua is very abundant along the south-west coast between Red Rocks 

 and the Old Boat-house, and often forms a narrow zone below Pelvetia on 

 the steep rocks. It is also found on the cliffs behind the Needles at the 

 same level, and on the rocks of Broad Strand. The species, in which the 

 thallus consists of small, scattered ridges, seems to be characteristic of steep 

 rook-faces, in rather exposed parts, usually growing with Lichina pygmaea 



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