14 6 Proceedings of the Royal Irish Academy. 



Many of the specimens were unfortunately sterile, and could not be 

 determined ; the fruits were there, but the spores were scattered. 



An alpine species, Pertusaria gyrocheila, was submitted to me lately by 

 Mr. W. "West, who had found it growing in great abundance on Slievemore, 

 Achill. The fruits are rather large, of a labyrinthine or gyrose form, and are 

 borne on raised, scattered pustules. It was originally collected by Carroll on 

 Ben Lawers, and described by Nylander in " Flora," 1865. Mr. West has also 

 collected it on the mountains of Harris on the West of Scotland. These were 

 its only previous records. 



Some specimens of Usnea were collected both from trees and from rocks. 

 They were poorly developed and somewhat difficult to determine. 



Several species of Verrucaria and allied genera were found only once. They 

 are easily overlooked by the most careful collectors ; and are probably fairly 

 common and abundant. 



The distribution of lichens is ecological even more than geographical. They 

 are intimately associated with their substratum, each growing generally on its 

 own special rock, tree, or soil. Some few grow indiscriminately where they 

 can find conditions favourable to their development. As a rule they avoid too 

 shady situations, and they are to be found in most profusion on the sunny side 

 of tree or wall. The green algae, often deeply seated in the thallus, require 

 the light rays at their highest intensity, these being often obscured by the 

 pigments — protective or otherwise— of the cortical cells. Some species never 

 leave the shore ; others are almost entirely confined to mountain-tops. Each 

 species has its chosen locality as well as its favourite habitat. They clothe the 

 rocks with a soft and variegated colouring, or lend a darker shade to the frown- 

 ing cliffs by the sea. Everywhere they add their share to nature's infinite 

 variety. 



In compiling the lists of lichens we have followed the classification of the 

 two parts of the Monograph of British Lichens published by the Trustees of 

 the British Museum. They are known and used by British lichenologists, 

 although Part I. is now somewhat out of date. The species new to Ireland, 

 as far as could be ascertained, have been marked with an asterisk. Use has 

 been made of Mr. Adams's lists in questions of distribution. We do not claim 

 to have exhausted the lichen flora of the district, but only to have given a 

 representative list of these plants, many of them very difficult of detection. 

 My warmest thanks are due to all who have given generously of their time 

 and skill. 



