15 40 Proceedings of the Royal Irish Academy. 



1. Exposed Cmws.-^-Several of these occur between Portlea and the light- 

 house, and are accessible at low tide. The walls, almost up to the roof, are 

 covered with encrusting organisms representing algae, lichens, and sponges ; 

 and except for local patches, shrubby species are absent. In the following 

 list, the first four are dominant, occurring roughly as bands from above 

 downward in the order mentioned, whilst the three last are scattered 

 Irregularly a short distance above high-water mark : — 



Hildenbrandtia prototypus. . Lithothamnium laevigattim. 



Yerrucaria sp. Ralfsia clavata. 



Lithothamnium Lenormandi. Cruoria pellita. 

 L. polymorphum. 



Large sheets of sponges also occur, and amongst these Halicfamdria 

 pa nicea, frequently with Rhizoclonium Kerneri f. cndozoica, is abundant. 



Small patches of a very short growth of the following fruticulose species 

 are occasionally found, their presence probably indicating local shelter : — 



Phyllophora rubens. Plumaria elegans. 



Chylocladia ovalis. Corallina officinalis. 



Where fresh water exudes from the roof or walls, streaks of Cladophora 

 mpestris, if the exposure be not too great, mark its presence, and at times 

 Rhodochorton fiorididum in addition. Pools are generally lacking; if present, 

 their flora resembles that given below for sheltered caves. 



2. Sheltered Caves. — Several types of these may be distinguished according 

 to the nature of the shore and the manner in which they receive protection. 

 In our area the two following only need be mentioned: — (a) Open caves 

 on exposed coasts, protected by rocks at the entrance (Roonah Point) ; 

 and (b) high-level caves with the entrance at, or just above, high-water 

 mark. In the former there is often a variety of ground and vegetation, 

 especially if boulders and pools occur ; in the latter the conditions arc more 

 uniform. 



(a) The encrusting vegetation at Roonah Point is the same as that on 

 exposed coasts, but less extensive; the mossy growth of Rhodochorton Rothii 

 is abundant on the drier boulders and on the upper parts of the walls ; 

 Sphacelaria britannica and various Cyanophyceae occur with this species, and 

 Phyllophora Traillii is found in patches. An abundant growth of shade- 

 loving Florideae follows at a lower level, covering rocks, boulders, and 

 shallow pools, Chyloeladia articnlata, Delesseria alata, Nitophyllum laccrahim, 

 Pol ysiphonia urceolata, and encrusting species such as Lithoth" milium 



