206 Proceedings of the Royal Irish Academy. 



have been gathered chiefly in Ireland, and especially in the neighbourhood of 

 Cork, where the moist, smoke-free atmosphere favours the luxuriant growth 

 of these and other corticolous lichens. 



The author is indebted to Miss M. C. Knowles of the National Museum, 

 Dublin, for identification and confirmation of the specimens used. 



II. — Selection of Species. 



The numero • are grouped by Zahlbriickner into the 



sub-genera Hypogymnia, M- and Euparmelia. Of these the two 



former possess no distinct rhizines. their under-surfaces being described as 

 naked. It is evident, however, that attachment must be brought about by 

 some means, and that, considering the presence of some of these forms on the 

 uppermost branches of trees in windy places, this attachment must be very 

 close. The method will be illustrated by the species P. Physodes. 



Of the sab-genus /.' . those sections which bear numerous true 



rhizines may be divided according as the rhizines reach the edge either in 

 their normal form or in a rudimentary, papillose condition, or are confined to 

 the middle, being absent at the edge or represented by cilia. 



To the first class belong the Becti mielia and Hypotrachynia. 



The former comprisi _ a yellowish colour in the upper 



surface, and will be represented by /'. - srsa; the latter includes the 

 white, grey or brown members, and is illustrated ; P. vatilis, P. Sorreri, 

 P. 



the se< sa belongs the section .1 ■■'■'.'■ inter, including 



- '-')')• 



til.— Description os Attachment Organs. 



1.7' ' /.. i. 



Tins species, as stated above, lias no true rhizines. The further diagnostic 

 1 by Lindau — that of the separation of the lower cortex from 

 the medulla _ in empty space — i o older specimens and to 



the portions of these which are not in contact with sub-strata to which 

 adherence i- ger thalli or thalline lobes, especially if in 



contact with a - ice Buch as wood, bark or moss, show a lower 



cortex either less definitely developed than the upper or even entirely 

 absent. 



The hyphae of the medulla turn from their normal horizontal direction 

 an^l _ - into tl itum in the manner described for the 



