15 38 Proceedings of the Royal Irish Academy. 



Island (as in S. England) is composed of two species — N. multifidum, and the 

 stouter unbranched N. elminthoides Batters {=N. lubricum J. Ag.). 1 The zone 

 formed is 5 to 6 feet deep, and extends from about half-tide level to the ordinary 

 low-water mark. Its luxuriance varies considerably in different localities. 

 In some, a vigorous growth is present in the upper part of the zone, whilst 

 in others the algae are better developed near low-water mark. N. elminthoides 

 is usually confined to the upper portion, and lasts later in the season than 

 A r . midtifida. The plants are attached to bare rock, or limpets, and 

 occasionally to mussels. They prefer sloping surfaces, fully exposed to 

 waves and surf. 



The Nemalion association is found in the band of Lithophyllum incrustans ; 

 but it prefers bare rock devoid of other vegetation. Where mussels occur, it 

 is usually replaced by the association of Ceramivm acantJwnotum, or 

 Khodymenia. Amongst it are scattered individuals of Scytosiphon lomentarius, 

 Enteromorpha compressa, Bhizoclonium implexnm, and Polysiphonia Brodiaei, 

 the last-named being confined to the lowest levels. On Clare Island the 

 association is of frequent occurrence ; and in Clew Bay it occurs on exposed 

 points, such as Old Head. A similar type of growth has been described by 

 Kjellmann (78), and Kylin ('07), for west Sweden ; by Gran ('93) for Norway ; 

 it would appear also to be widespread in Denmark {vide Rosenvinge, '09). 

 In the south of England the community is frequently met with, having been 

 noted by me on the coasts of Dorset, Devon, and Cornwall. 



Himanthalia Association. 



This familiar association, which is well developed on Clare Island, is 

 characteristic of moderately exposed shores. It forms a belt in the lowest 

 part of the littoral region ; but the extent of its horizontal range varies with 

 the amount of slope and the nature of the coast. On steep and vertical 

 rocks it is absent, or exists as a narrow band, 1 foot deep. On a shore of 

 moderate slope the band is wider, and extends from the Laminaria zone to 

 2 or 3 feet above low-water mark ; whilst on flat shores, especially where 

 there is a dense sub-vegetation, it covers a wide area. With partial shelter, 

 Himanthalia descends some distance into the sub-littoral region, and occurs 

 mixed with Cystoseira ericoides and species of Laminaria ; but apart from the 

 extension both in an upward and downward direction, its normal position 



1 This plant, clearly figured by Velley, is usually regarded as a distinct species ; but as seen in 

 Clare Island and in the South of England, it is difficult to separate from N. multifidum. 



