16 40 Proceedings of the Royal Irish Academy, 



- The species concerned are as follows : — .'■■'. 



Corallina squamata, dom. 



C. officinalis, co- or sub- dom. 



Lithothamnium Lenormandi. \ 



, . , , „ . Undergrowth, 



Liitnypnyllum incrustans. 



. in zones. 



Lithothamnium polymorphum. j 



(a) The Corallina growth is very much worn down by the waves, so that it 

 occurs in the form of dense cushions, the specific identity of which is difficult 

 to ascertain. In shallow depressions or with slight shelter, the production 

 of larger and more perfect fronds allows their true nature to be determined, 

 and in each case examined it was evident that the bulk of the growth was 

 composed of C. squavwta, though 0. officinalis was at times also present. 



The first signs of the Corallina belt are found at about half-tide level, 

 usually just below the top of the Nemalion zone. The plants are found here 

 in chinks and fissures, where there is little risk of drying, and on passing 

 downwards they gradually spread out over the surface of the rocks. They 

 are, especially in the upper parts, frequently attached to mussels ; and the 

 growth of these two organisms together form the compact cushions referred 

 to. At the lower part of the zone the fronds are large. This is due 

 partly to their being protected by the Laminaria foliage, and partly to their 

 being below the level at which the waves break. A great improvement in 

 colour is at the same time noticeable. C. sqiiamata as well as C. officinalis 

 occurs at the top of the Laminaria belt ; and the latter certainly, if not indeed 

 both, descends some distance into the sub-littoral region. 



With increased shelter, though the plants are larger and less broken by 

 the waves, the band as a whole is not so conspicuous, owing to its being 

 replaced by other algae (usually Laurencia). Shallow pools are an exception. 

 Here a fine growth of C. officinalis is often present, and less frequently 

 C. squamata. The latter is seen at its best on narrow ledges, or hanging from 

 the sides of shady rocks. 



The Corallina association above dealt with differs floristically from all 

 others hitherto described, in being composed largely of the southern species 

 C. squamata. This is probably the case in all the warmer parts of the British 

 Isles. There is no question as to the abundance of C. squamata in Clare 

 Island ; and it is doubtless equally common along the whole of the south and 

 west of Ireland. It also occurs in plenty in the south of England, and has 

 been noted as forming the principal constituent of the Corallina association 

 at the end of Portland Bill. 



(b) The Lithothamnium vegetation is described here together with that of 

 Corallina, because it is exceptionally well developed when found in company 



