Clare Island Survey — Marine Algae. 15 107 



No. 91. 



This well-marked plant occurs abundantly at the bottom of the hill-side 

 streams which flow into Achill Sound and Bellacragher Bay. It grows 

 attached to stones or other algae such as F. ceranoides, and though flooded 

 by every tide, it is for the greater part of the day immersed in fresh water. 

 A certain amount of growth occurs above the average high- water line ; and 

 this is bathed in salt water at spring tides ; but the plants are small, and the 

 growth very poor, compared with that of half-tide level. The lower limit is 

 at or slightly above low-water mark. Monostroma gives the stony beds of 

 the Bellacragher torrents a deep green colour in spring ; but in other streams 

 (e.g. to the north of Achill Bridge) the beds are muddy, and the alga 

 occurs only on the stone fords or where there is good means of attachment. 

 The growth is found in spring, summer, and autumn ; in February, 

 also, a certain amount was visible. The maximum is reached in April and 

 May, at which season it extends to the stones and Fuci on the flanks of the 

 streams (see also p. 87). 



The plants themselves are of a deep green colour, growing in rosettes 

 or dense tufts, regularly orbicular at first, but becoming more or less lobed 

 or even lanceolate later. They are usually 5-8 em. across; but lobed 

 specimens reach a length of 15-18 cm. The thallus is thin, that of the 

 adult plant seldom measuring more than 20-25 n thick, and the cells 

 small, about 10-15 xfi/i in section; but in young plants they are often 

 larger. It adheres very well to paper, even in the dry air of the herbarium. 

 The plant has only been found attached, as detached specimens are swept 

 down by the stream and carried away ; in a free state, it would probably 

 reach a larger size. 



With regard to affinities, the plant agrees in structure with 

 Thuret's M. laceratum; but he describes this as floating in ditches 

 with Obione. From M. orbictdare, so common near Belclare, it differs 

 in its smaller size and thinner frond ; but it is possible that this is 

 due to its peculiar habitat. On the other hand, the plant may be regarded 

 as a small attached form of M. latissimum, or as a distinct species peculiar 

 to the situation referred to. .„:-.. 



No. 95 (= M. crepidinum Fallow (). 

 The second species left unnamed occurs on the banks of the streams 

 on the sandy shore at Mulranny, and at the mouth of the Bunowen at 

 Louisburgh. It is attached to the stems of Ascophyllum and F. vesiadosiis 

 (especially on the under branches), but is also found on the stones and rocks 

 covered by these algae, and occasionally in the open. The plants are always 



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