114 Scientific Proceedinrjs, Royal Dublin Society. 



The partiality of V. mucosa for smooth surfaces is plainly seen on the 

 Broad Strand. On tlie smooth boulders at Stella Maris it covers a wide area 

 with an almost pure growth ; but below Earlscliffe, where the foreshore is 

 mainly bed-rock of various textures and of different heights and degrees of 

 smoothness, V. mucosa forms an interrupted growth, and occurs chiefly on the 

 harder rooks and smoother surfaces. V. microsi^ora is much more abundant 

 on this part of the strand. Similarly on the cliffs, V. mucosa seems to be 

 altogether absent from the grits. In tliis connexion it is worth noting that I 

 recently explored a small tract of the coast of Antrim near Fair Head, where 

 the rocks are coarse Carboniferous sandstone, without finding any trace of 

 V. mucosa; while V. microspora, Lichma pygmaea, and Arthopyrenia hahdytes 

 were abundant. 



The details as to the habitat and distribution of V. mucosa in other 

 countries are exceedingly meagre. Weddell, who searched the shores of I'lle 

 d'Teu in vain for it, says it has been observed on the coast of north Europe, 

 but that the only actual localities from which it is known in France are in 

 the neighbourhood of Cherbourg, where it grows on stones in the beds of 

 small rivers or streams flowing into the sea, in places where the current is 

 most rapid. This habitat is rather similar to that in which V. aquaiilis 

 grows on the Howth coasts, but, though carefully looked for in places where 

 fresh water flows, V. mucosa was nowhere met with on these coasts. 



Arthopyrenia halodytes has such a wide vertical range, and grows in such 

 a variety of situations, that it is very diflieult to say what is the natural 

 habitat of this species on the Howth shores. In so far as it enters into the 

 composition of the V. maura belt, its distribution has been gone into already 

 and is very similar to that given by Weddell for the coasts of I'lle d'Teu, 

 where it is chiefly associated with V. maura and L. confinis. On the Howth 

 coasts A. halodytes has a much wider vertical range, but it seems to be most 

 abundant just above and below high neap-tide level. In the lower Verrucaria 

 belt it is usually associated with Verrucaria microspora and V. striatula i. 

 continua. On sunny sheltered shores both A. halodytes and V. microspora 

 are common amongst the Pelvetia growths, and on Broad Strand extend from 

 this level down as far as low neap-tide. A. halodytes, is however, much 

 less abundant at low levels than V. microspora. On steep rocks, at several 

 places between Red Rocks and Old Boat-house, A. halodytes sometimes forms 

 a narrow warm-brown band on the rough quartzites between V. maura and 

 Pelvetia, but it also grows with V. microspora and V, striatula, f. continua, 

 in the Pelvetia belt and at lower levels on these same rocks. On the more 

 exposed coasts A. halodytes is less commonly seen in the lower Verrucaria 

 belt. A. halodytes var. tenuiscula is found at various places on the south 



