Knowles — The Maritime and Marine Lichens of Hoivth. 117 



with a close mat of Laurencia pinnatifida and Gigartina mamillosa, left very 

 little unoccupied space for the lichens to grow on. 



The surface of tlie apparently bare rocks lying along the top of the beach 

 at about high neap-tide level, when examined with a lens, was seen to be, 

 thickly dotted with the little black fruits of Arthopyrenias. Two species — 

 Arthojyyrenia litoralis and A.foveolata — were abundant and were met with 

 throughout the whole neap-range. There is literally hardly an inch of bare 

 rook that they have not colonized ; A. foveolata is most usual on rocks in 

 the upper levels ; nearer low water it grows indifferently on the rock and on 

 barnacle shells; if anything, it is more abundant on the barnacles. A.foveolata 

 is more general than A. litoralis in the upper part of the beach, its insculpt 

 perithecia being better adapted to withstand the drier conditions. It is usual 

 on flat surfaces, while A. litoralis, which has prominent perithecia, grows 

 most often on the sides of the rock and in more shade ; nearer low- 

 water both species are to be found on the most exposed noses of the strata. 

 Both species prefer a rather soft substratum, and are more frequently seen on 

 the pale grey limestone ; where they occur on the dolomites it is usually on 

 the embedded fossils. On the south and south-west coasts A. litoralis and 

 A.foveolata are also found, but only on barnacle shells never on the rocky 

 substratum ; A. foveolata is very abundaut on these coasts ; A. litoralis is very 

 rare. 



The Verrucarias, so common on the south and south-west shores, are very 

 poorly represented on the limestone. V. mucosa and V. microsjMra were the only 

 species met witli. They are entirely absent from the upper part of neap- 

 range, and only make their appearance about the middle of the Fucus serratus 

 belt, occurring as thin patches here and there under the shade of the algae. 

 They extend down the shore as far as low-water, and are most usual on the 

 harder dolomites. Verrucaria Lorrain-Smithii, a new species, not seen on 

 the silicious rocks, was associated with them near low-water. This last species 

 is extremely inconspicuous and difficult to detect ; the thallus is very thin, 

 sometimes evanescent, and the perithecia so very minute that they can only 

 be seen with a strong lens. The absence of gelatinous species from the 

 • upper part of the shore may be due to the fact that calcareous rocks dry up 

 much more quickly and are more easily heated thau silicious strata. 



A few tufts of Lichina confinis were seen on the dolomites in the south- 

 east corner of the Harbour ; V. microspora, too, was present here, but the 

 growth was very scanty. 



2. Terricolous Lichens. 



The earth-loving lichens do not seem to be very plentiful on the 

 Howth coasts. In certain localities they cover fairly large areas, but 



