15 60 Proceedings of the Royal Irish Academy. 



south coast of England; and though not recorded from other countries, it 

 probably exists, at all events, on the north of France. 



Ehodochorton floriduluni Association. 



Small patches of this are occasionally found on rocky shores ; but it is 

 characteristic of the sand and low-rock series described later (p. 65). 



Sand-Pool Vegetation. 

 Occasionally met with, but typically developed on sandy shores 

 (see p. 67). 



Cave Vegetation. 



The caves of sheltered coasts are dealt with on p. 46. 



(b) Sub-liltoral Region. 

 Laniinaria Association (sheltered). 



The Laniinaria vegetation of sheltered shores is fairly well developed. It 

 is found in many parts of Clew Bay, in Bellacragher Bay, and in parts of 

 Achill Sound. The characteristic species are L. saccliarina and L. digilata, 

 the latter being, as a rule, confined to localities where current is present. In 

 the deeper and more open parts, L. Cloustoni exists ; but with the appearance 

 of this species L. saccliarina drops out, and the association passes gradually 

 into the exposed type. 



Whilst on exposed coasts the Laniinaria vegetation is typically in belts, 

 on sheltered coasts it is commonly discontinuous, and occurs rather in plots. 

 This is mainly owing to the scattered nature of the anchorage. It is found 

 wherever rocks or large stones occur ; and the amount is determined by the 

 extent of the stony area. In Clew Bay, the hard bottom is found in three 

 kinds of ground, each of which supports a different type of Laniinaria 

 vegetation. As the latter are determined by definite ecological conditions, 

 and as, in Clew Bay, they scarcely overlap, it is reasonable to regard them as 

 three sub-associations. 



The sub-association of Laniinaria saccharina (most often var. latissima) 

 occurs in the inner part of the bay, where the conditions are quiet and the 

 current weak. The fronds are long and very broad — in extreme cases up to 

 a yard across. Occasionally the association is pure (except for small species 

 forming the undergrowth) ; but as a rule other algae intrude, such as 

 Cystoseiro granulata and Hulidrys siliquosa. Barely the association merges 

 into the Zostera beds. The second sub-association is characteristic of ground 



