Knowlks — The Marihme and Marine Lichens of Hoivth. 115 



coast. It grows chiefly on the hard smooth qnartzites, sometimes appearing 

 as small light-coloured patches amongst the V. mucosa growths. 



The chief requirement of A. halodytea seems to be a moist situation ; and 

 on tlie Howth coasts it appears to be rather indifferent as to wliether the 

 moisture is salt or fresh water. 



Algologists have usually grouped V- maum and the marine licliens with 

 Hildenbrandtia, and have treated them as one association. Borgeseu (2, p. 711), 

 in describing the "Hildenbrandtia formation" on exposed coasts of the Faeroes, 

 says : "It covers the rocks with a dense mat of various colours to a considerable 

 height, i.e. up to more than 2 feet above the level of the sea and down into 

 the coralline formation. The uppermost part of it mostly consists of lichens 

 which, according to the Rev. Deichmann Branth, belong to different species 

 of Verrucaria." A. D. Cotton describes a similar vegetation as growing on 

 the coasts of the Clare Island Survey district, from both exposed and sheltered 

 shores, under the name of the " Hildenbrandtia- Verrucaria Association," and 

 suggests including in the association all the littoral encrusting species that 

 are soft and not calcareous. He mentions Verrucaria maura, V. mucosa, and 

 HildenbrancUia prototypus as being the characteristic species. 



On the sheltered Howth coasts Hildenbrandtia has the same distribution 

 as the lower Verrucarias, extending throughout neap-range, being most 

 conspicuous and best developed nearer low-water mark, while the Yerru- 

 carias form a more continuous growth on the upper part of the shore. The 

 red or yellowish-red crusts of Hildenbrandtia form such a striking contrast 

 in colour to the green and blackish-green thalli of the Verrucarias that it is 

 a comparatively easy matter to trace their distribution. They seem rather 

 to form two overlapping belts, Hildenbrandtia ascending the beach and 

 extending its range upwards under the protection of the larger algae or by 

 occupying the bottoms of shallow pools or the cracks and crevices in the 

 rocks ; the Verrucarias, on the other hand, taking advantage of every bare spot 

 to penetrate further towards the sea, in the lowest parts colonizing those 

 projections that are first exposed to sun and air as the tide retreats. On 

 the cliffs the true sequence of the two belts is more easily seen. In the 

 small cave referred to, page 113, Hildenbrandtia forms a distinct zone on 

 the walls below Verrucaria mucosa, just inside the entrance; and at 

 various other places near the Needles Hildenbrandtia also mainly occurs 

 below the Verrucarias, both growths rising liigher in shade than in the more 

 open situations. On the more exposed and broken parts of the coasts 

 Hildenbrandtia may occasionally be seen in the Verrucaria maura belt ; but 

 where this is so, the two plants live under quite different conditions ; moisture 

 and shade seem to be necessities for the Hildenbrandtia, and at this level it 



