15 *>4 Proceedings of the Royal Irish Academy. 



de sel Bans melange de vase. Ed eel ctat il forme des assises diversement 

 colorees, accumulees but une epaisaeur parfoia considerable et dont Lea 

 supeneuree, qui bohI lea Beulee vivantes, peuvent fetre detachees par largee 

 plaques el roulees comme dee morceaux de drap. Ce vegetal m£rite 

 done completemenl le nom de chthonoplastes (constructeur du boI) «pi i 

 lui a etc donne* par lea premiere observateurs." 



In Clew Bay the Microcoleus association was usually found where there 

 was a certain amounl of mud. It occurs in lame patchea at Mulranny and 

 also in the Belclare neighbourhood. In the small bay to the north-weal of 

 Ailnll Bridge it forms a broad band just below high-water line, binding tin- 

 upper layer of mud into a firm sheet. It was also noted in several localities 

 in fairly pure sand, but only as covering small areas. 



Various other blue-green algae enter into the composition of the 

 iation, notably : — 



In upper parte : In lower parte : 



Lyngbya aestuarii. Vaucheria Thuretii. 



I j. lutea. Rhizoclonium riparium. 



Microcoleus tenuis. Enteromorpha torta. 



Vaucheria Thuretii Association. 



This vegetation takes us further still from the pure sand, being found only 

 where there is a considerable proportion of mud. Future work will probably 

 show that it should be regarded as an association in the mud-formation. 

 V. Thuretii tonus a dense mossy growth embedded in the matrix, and appears 

 to cover very extensive areas. Several samples were taken both from dew 

 Bay and from the muddy inlets north of the bridge at Achill Sound : and in 

 each case the mossy tuft consisted of this species, often in beautiful fruiting 

 condition, and practically pure. The growth is always immersed, the tips of 

 the filaments alone Bhowing, thus differing markedly from /'. eoronata, which 

 tonus a clean velvety growth. Felts composed of Rhizoclonium, Chaetomorpha 

 and Cladophora fracta often lie on top of the Vaucheria, and these, in many 

 cases, appear to be attached, and not merely drifted fragments; so that it is 

 possible thai careful study would reveal definite societies of other -)■• 

 amongst the general vegetation of Vaucheria. 



The vertical range of V. Thuretii ie determined by the extent of the sandy 



mud. It flourishes in the lower part of the littoral region, ami probably 



nds to low-water mark. Its upper limit is usually immediately below 



/•; spiralis, but whether this was due to the lack of sufficient mud or to othei 



causes in addition (euch a- long exposure to the air) was not ascertained. On 



