15 70 Proceedings of the ttoyal /risk Academy. 



an important part in the formation of coral reefs. But notwithstanding 

 the many references, both systematic and biological, to this type of 

 vegetation, it is nol by any means easy to compare the Lithothamnium flora 

 of one country with that of another. This is owing to the deceptive nature 

 of morphological characters, and to t ho many erroneous determinations in 

 the past. Foslie has left reliable records for recent years, and the anatomical 

 classification elaborated by Dr. Lemoine promises more success for the 

 future. 



Between the outer islands of Clew Bay areas of Lithothamnium calcareum 

 ("coral- banks") are common. They arc found on a soft but firm bottom, 

 consisting usually of Btones and shells on sand, though occasionally Litho- 

 thamnium may be dredged where there is a thin layer of mud. The usual 

 depth in which the hanks occur is 1-5 fathoms, and here and there the plants 

 may be gathered by hand during the lowest tides. The association is com- 

 posed of the Eollowing species: — 



lithothamnium calcareum. dom. 

 Lithophyllum fasciculatum, locally sub-dom. 

 L. incrustans. 



L. incrustans var. subdichotomum, rare. 

 Lithothamnium norvegicum, rare, 



In many places L. calcareum forms a pure growth extending over a con- 

 siderable area, but in others it is mixed with L. fasciculatum, and sometimes 

 all four species occur mixed together. A characteristic growth of epiphytes 

 accompanies the vegetation, of which Polysiphonia subulifera, Pterosiphonia 

 parasitica, Aglaozonia reptans, Spacelaria cirrhosa, Rhodochorton Jloridulum, and 

 Gelidium sp. are the most constant. Dictyota, Chylocladia kaliformis, and 

 Laurencia obtusa are also abundant in summer. 



Wiih trivial variations this is the type of fruticulose Lithothamnium 

 vegetation found throughout Clew Bay. It presents one remarkable floristic 

 feature, namely, the presence of L. fasciculatum, a species which is only 

 known from the west of Ireland. Another interesting plant is L. incrustans, 

 var. subdichotomum, an alga which was formerly regarded as L. dentatum, but 

 shown by Dr. Lemoine in the present report to be a detached and rolling 

 form of the common species, L. incrustans. 



Other lAthothamniv/m banks in Ireland and Great Britain. — It was of 

 interest to find that the Clew Bay association agreed exactly in its 

 composition with that which had been described for Roundstone. The latter 

 district is the original station for L. fasciculatum i and Foslie, when working 

 out the European Lithothamnia, paid a special visit to the locality and 



