15 6 Proceedings of the Royal Irish Academy. 



which for comparative purposes is of the very greatest importance, I 

 have availed myself freely of the help of specialists. Dr. Kuckuck kindly 

 worked out the ITalfsiae, and cheeked a number of other members of the 

 Phoeophyceae. The weight of his authority in doubtful cases was most 

 valuable. I am also much indebted to Dr. M. Lemoine. Since the death of 

 Foslie, the identification of encrusting Lithothamnia was uncertain work, 

 owing to the confusion in the literature, and the scarcity of reliable material 

 in British herbaria. Madame Lemoine willingly undertook to examine the 

 Irish material, and, by her method of anatomical investigation, to work out 

 and compare critical species with authentic specimens. Though no important 

 additions to the list have resulted, it is highly satisfactory to have trust- 

 worthy identifications. An interesting point with regard to geographical 

 distribution has, moreover, been cleared up by her. Dr. K. Kosenvinge kindly 

 determined the Chantransiae, whilst Prof. N". Wille, Prof. C. Sauvageau, and 

 Dr. H. H. Peterson examined the species of Ulothrix, Spacelaria, and 

 Ceramium respectively. Prof. G. S. West's opinion on the brackish and 

 freshwater species, and Mr. J. Adams' aid in connexion with the distribution 

 of Irish plants were most helpful. Mr. E. M. Holmes has taken the keenest 

 interest in the Clare Island Mora, and throughout the work of identification 

 has always most liberally bestowed the benefit of his valuable and unique 

 experience. To all these botanists I offer my sincerest thanks. Special 

 acknowledgments are due to Mr. E. Lloyd Praeger, the organizer and 

 secretai-y of the Survey, to whom I am deeply indebted for advice on matters 

 botanical and geological, as well as for encouragement and assistance in a 

 number of ways. 



I.— THE EXTEKXAL COXDITIOXS-OF THE AKEA. 



1. — Climatic Conditions. 



1. Atmospheric Temperature and Moislwre. — The insular climate of Ireland, 

 and the influence of the Gulf Stream drift, combine to render the Clare 

 Island district particularly mild and damp. In winter rough stormy weather 

 prevails, together with a large amount of rain, but frost is rare. In summer 

 the weather is changeable, rain and gales from the south-west are frequent, 

 and the average temperature relatively low. Though occasional warm days 

 occur, spells of hot dry weather arc most unusual ; and this renders the 

 intertidal region more favourable for vegetation than that of the south coast 

 of England. A glance at the isotherms of Europe shows that the mean 

 January temperature of 43° F. (=611° C.) corresponds with that of the south 

 of France and the north of the Adriatic; whilst the July isotherm of 5S r F. 



