15 20 Proceedings of the Royal Irish Academy. 



square yards. Both possess exceedingly thin encrusting thalli, which are so 

 closely adpressed to the rock, that the latter appear as if coated with paint. 

 In addition to those mentioned above, probably several other species of lichens 

 are present. Of the three plants referred to, V. maura forms a band a short 

 distance above the Pelvetia zone, whilst the other two appear below Pelvetia, 

 and descend nearly to the level of low-water. Hildenbrandtia is more 

 susceptible to drying up than V. mucosa, and in the Pelvetia and F. spiralis 

 zones it occurs under the shade of algae, in damp chinks, or in pools. On 

 ordinary open shores its growth does not occur above this level ; but on very 

 exposed coasts when there is spray, it ascends far above high-water line, 

 being found in dark fissures in the rock, or in small pools that occur on the 

 rugged cliffs, the water of which is often brackish. On the lower part 

 of the shore Hildenbrandtia is not confined to pools and chinks, but is found 

 on bare rocks, and remains quite dry for several hours. In the lowest 

 levels, it is usually replaced by a broad band of Balfsia clavata, in which 

 patches of Petrocelis eruenta are frequent, especially if the rocks are 

 smooth. 



Vcrrucaria mucosa grows mostly on half-tide rocks that are fully exposed 

 to light and air ; in shady positions or where a covering of algae prevents 

 excessive desiccation, the growth extends to the F. spiralis zone; but it 

 rarely, if ever, takes advantage of pools to ascend to a higher level. In this 

 respect it differs from Hildenbrandtia. The plant prefers smooth rocks or 

 boulders, and is seen at its best on the beach north of Portlea, where it 

 covers the upper sides of the boulders from about half-tide level to below 

 the low-water limit of neap-tides. Its growth here is almost pure, and 

 the individual patches are very large, some noted measuring a yard 

 across. The vertical range on the shore varied somewhat in the different 

 localities ; but this may possibly have been due to the presence of more than 

 one species. On only one or two occasions was a Verrucaria-growth noted 

 in a rock-pool. Probably few lichens are so difficult to determine or so 

 little understood as the marine Verrucariae ; and it is a source of great 

 satisfaction to learn that Miss M. C. Knowles is working at the problem, 

 and doing so from an ecological as well as from a systematic standpoint. The 

 encrusting algae also are in need of critical study. 



The present community is well developed in all parts of the survey-area. 

 It is abundant on smooth slabs and boulders, and is also found on the rough 

 slate and sandstone. It extends to sheltered localities, where, if rocks and 

 boulders are absent, it often occurs on stones and pebbles. A very similar 

 vegetation exists in Sweden, Iceland, and the Faeroes, according to the 

 accounts of Kylin, Jonsson, and lioryesen. 



