THE SEA SHORE 31 



water mark by a broad belt composed of several kinds of 

 Laminaria, the largest of the brown weeds which has long 

 fronds, very broad and without a mid-rib, and is secured to 

 the rocks by a massive " hold-fast." They are never 

 exposed except at the lowest spring tides. 



A number of other weeds are common on the shore, and 

 can most conveniently be referred to now. The green 

 weeds are especially widespread, the " Sea lettuce " 

 (Ulva lactuca) with broad, delicate fronds and living in 

 pools usually above half-tide level, and Cladophora rupestris 

 of a darker green and bushy compact growth which is 

 common in pools everywhere. An easily recognized brown 

 weed commonly exposed between tide-marks is Himanthalia 

 lorea, which has peculiar cup-shaped attachments to the 

 long narrow fronds, while of the red weeds, the "Dulse" 

 [Rhodymenia palmata) which has fiat, irregular crimson 

 fronds, and " Carragheen " [Chondrus crispus) (Plate 

 127) with thicker dark reddish-brown fronds, which 

 appear blue when seen in certain lights, are the commonest, 

 occurring in the upper and lower regions of the shore 

 respectively. The latter is eaten in certain parts of Ireland. 

 Frequent in rock pools are the pink encrusting corallines 

 (Plate 8), not at first easily recognized as sea weeds for they 

 have limy skeletons like some of the encrusting animals. 



Now let us consider some of the animals which live on 

 rocky shores. They may be divided roughly into four 

 categories, those which live exposed on the surface of 

 stones, rocks, or weeds, those found under stones, those 

 which live in holes and cracks in the rocks, and those 

 inhabiting rock pools. Of the first group the most char- 

 acteristic members are the sessile acorn-barnacles (Balanus) 

 which cover the rocks with a carpet of little sharply pointed 

 pyramids, especially near high- water mark where they form 

 a definite Balanus zone (Plate 10). Here too are many 



