Clare Island Survey — Marine Algae. 15 67 



Corallina-Cladosteplms Community. 



This vegetation is frequently very well developed on sandy shores where 

 low rocks are present {e.g., Old Head). It retains a certain amount of sand, 

 but is usually found on raised or sloping rocks where the quantities deposited 

 are small. The community clearly forms a connecting link between the sand- 

 and rock-formations ; but as both the species composing it are distinctly 

 saxicolous, and do not form rhizoids, it is regarded as belonging to the latter, 

 and is dealt with on p. 58. 



The Porphyra umbilicalis Community. 



Though attached only by a basal disk, and clearly belonging to the rocky- 

 shore formation, P. umbilicalis var. laciniata is frequently found, fringing 

 the sides of half-buried rocks, on sandy beaches. Its growth in this habitat 

 is described on p. 57. 



Vegetation of Sand-Pools. 



A very interesting psammophilous flora occurs in pools amongst low rocks 

 on sandy shores. The plants are not small and filamentous, such as Kho- 

 dochorton or Vaucheria (pp. 65 and 64), but large and bushy ; hence, though 

 partially embedded in sand, they are invariably fixed to underlying rock. 

 Polyides and Gracilaria may be taken as typical examples ; but some six or 

 eight other species occur, all being sand-loving plants, and found as a rule in 

 the sub-littoral region. When, as is often the case, ordinary rock-pools are 

 absent, the constancy of this sand-pool vegetation is very manifest. 



Algae which thrive under such conditions have, as would be expected, 

 much branched thalli of erect habit. The fronds are more or less terete, and 

 in many cases tough. But other forms occur, especially where the amount of 

 sand is not excessive. Sand-pools are found at Old Head,, and between that 

 spot and Leckanvy ; also to a certain extent near Mulranny. The typical 

 flora is as follows : — 



Polyides rotundus, c. Gymnogongrus Griffithsiana, r. 



Ahnfeltia plicata, c. Gelidium crinale, r. 



Gracilaria confervoides, c. Cladostephus spongiosus. 



Polysiphonia elongata, c. Corallina officinalis. 



P. atro-rubescens, c. Rhodochorton floridulum. 

 Furcellaria fastigiata. 



The last three are not characteristic of this vegetation only ; but they are 

 exceedingly common if the sand-layer is not thick, and, as shown above, 

 they form part of the littoral flora of the shore in question. The species of 



12 



