15 176 Proceedings of the Royal Irish Academy. 



DESCRIPTION OF PLATES. 



Plate I. 



Porpkyra umbilicalis association on south shore of Clare Island in July 

 (1010). The Porphyra belt at this spot takes the place of Fucus spiralis, and 

 occurs between the bauds of Pelvetia and F. vesiculosus, var. evesiculosus. It is 

 thus somewhat higher than usual. The shore is exposed and rather steep. 



Plate II. 



Boulder-beach between Portlea and the lighthouse, showing broken char- 

 acter of zones and associations. The Pelvetia belt is practically absent, and 

 the zones of Fvrvs spiralis and F. vesicidosus which follow are interrupted and 

 discontinuous. In the foreground Himanthalia with the usual undergrowth 

 of Lavrencia pinnatifida is seen, and also the beginning of the F. serratus 

 vegetation. Gigartina joins the Laurencia band in the lower levels, and 

 Ehodymenia palmata hangs from the shady sides of boulders. 



Plate III. 



Shallow rock-pool on south shore, half-tide level. Showing more or less 

 continuous covering of IAihophyllum imrustans with characteristic lip-like 

 protuberances (centre). Several tufts of Polysiphonia ' fruticulosa occur, and 

 in the upper left-hand corner Curallina officinalis and the more southern 

 C. sqvamata are seen together. To the extreme right is Polysiphonia Brodiaei 

 (upper corner). In pools of this kind small plants of Codium iiiucronatum 

 var. athinticum are frequent. 



Plate IV. 



" Coral beaches " in Mannin Bay, Co. Galway. The white sand of the 

 beach is composed of finely broken fronds of Lithothamnium calcareum, which 

 are washed ashore from the Lithothamnium association in the Bay. In some 

 beaches a few rocks are present, but these are largely devoid of algae (fig. 2). 

 The weed washed ashore in foreground is Zostera. Photographed at low- 

 water by Dr. G. H. Pethybridge, October, 1911. 



Plate V. 



Fig. 1. — Lithothamnium sand from Mannin Bay. Medium-grained sand 

 from the middle part of the beach (nat. size). At high-water mark the sand is 

 very coarse, and contains shells and Lithothamnium knolls ; at low-water it is 

 extremely tine, aud its origin is hardly discernible without a microscope. 



