Knowles — The Maritime and Marine Lichens of Hotvth. 113 



and F. mucosa. It is nowhere plentiful, and appears chiefly to grow only on 

 pure quartz rook and on the close-grained quartzites. On Broad Strand a 

 specimen tliat seems to be V. striatula was collected from the volcanic dyke 

 at low spring-tide level, but the spores were abortive. Both the species and 

 the form were noted on the coasts of Galway at Cleggan, growing in the 

 same way as on the Howth coasts — the species on steep shady rock-faces, in 

 rather exposed places, with Lichina pygmaea and V. mucosa, and the form on 

 both sloping and steep rooks, at the same level on the shore, but more in shelter. 

 Some of the most extensive colonies of Verrucaria mucosa seen on the 

 Howth coasts cover the boulders of the beacli at Stella Maris. This beach 

 below high neap-tide level is composed of rather small smooth quartzite 

 boulders, pretty much of a size. A belt of Pelvetia, about a j-ard wide, runs 

 along tlie upper part of ueap-range, and immediately below this Fucus 

 spiralis forms a band of thin growth among the boulders of nearly double 

 this width. The remainder of the foreshore is covered mainly by a wide bed 

 of Ascophyllum nodosum, which stretches down almost to low- water. In the 

 Fucus spiralis belt V. mucosa is very conspicuous as a continuous dark-green, 

 almost black band of greasy appearance, stretching along the shore, cleiirly 

 separated from the dull black band of V. maura, which covers the larger 

 boulders above it. Amongst the Ascophyllum plants every piece of bare 

 rocky surface is covered with the same dark greasy-looking stain. On the 

 upper part of the beach V. mucosa completely covers both the tops and the 

 sides of the boulders, but nearer low-water it is mainly found on the upper 

 surfaces, the sides being covered with the reddish crusts of Hildenbrandtia 

 prototypus. The growth of V. mucosa on this beach is almost pure, and 

 somewhat resembles that described by Mr. Cotton as covering the boulders 

 at Portlea, Clare Island. V. mucosa, however, reaches higher levels on the 

 more sheltered Howth shores, and has a wider vertical distribution. When 

 growing in shade tlie thallus of V. mucosa is of a bright green, and contrasts 

 with the darker colour of the lichen when found on flat rocks exposed to the 

 sun. In a small narrow cave in the cliffs behind the Needles, accessible 

 at low-water, the transition from the ordinary dark colour to the bright- 

 green shade-form is easily traced. Near the mouth of the cave V. mucosa 

 forms a dark band 4 feet wide on the sides, which gradually passes into a 

 band of brighter green as the light decreases. In the furthest recesses (the 

 cave is only about 15-20 feet deep) V. mucosa is entirely replaced by the 

 red alga Mildeiibrandtia prototypus, and a velvety growth of Bhodochorton 

 Botha covers boulders on the floor. On the north coast the sides of several 

 shallow caves exposed at low tide are covered in a similar way with a 

 beautiful emerald-green growth of V. mucosa. 



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