ZONES OF MARINE LIFE. 



411 



barnacles, often striping fhe sea-wall in a broad white band. 

 "Where the shore shelves a little, and rocky ledges decline 

 gradually into the sea, the common mussel delights to live, 

 firmly anchored by its byssal cable 

 in the crevices of rocks or among 

 masses of gravel, the pebbles of 

 which are tied together by its 

 silky filaments." The rock sides 

 and the floors of transparent pools 

 are here often thickly coated with 

 a nullipore, forming a hard pale Lnopet. 



red crust. The region of half-tide 



forms a third subdivision of the littoral zone, and is exceedingly 

 prolific in marine animals and plants. " Here we find Fucus arti- 

 culatus, with its graceful even-edged rich brown fronds, mingled 

 occasionally with the less elegant Fucus nodosus. Here limpets 

 throng, and dog-periwinkles (Purpura lapittus) crawl observ- 

 antly, seeking to bore more passive mollusks and extract their 

 juicy substance. This is the home of the best of periwinkles, 

 the large black Littorvna littorea, gathered in thousands for 

 the London market. On our western coasts 

 we find it in company with the purple-striped 

 top-shell (Trochus umbilicatus), and towards 

 the south with the larger Trochus crassus. 

 Here also sea-anemones love to expand their 

 many-armed disks, often glowing with the 

 most brilliant colours." A fourth sub-region 

 succeeds, the lowest belt above low-water 

 mark, and is distinguished by the presence 

 of the black saw-toothed sea-weed (Fucus 

 serratus), so much used in the packing of lobsters for market. 

 On its fronds creeps the lowest in grade of the periwinkles, the 

 variously tinted Littorina neritoides, exhibiting every colour in 

 its obtuse and thickened shell. 



" At the verge of low-water mark, immediately below it, where- 

 ever the coast is rocky, there are all round the British shores, 

 within a space of a few inches, a remarkable series of more or 

 less distinctly defined belts, each consisting of a different species 

 of sea-weed. These in succession are, the Laurenda pmnati- 

 fida uppermost* then the green Conferva rupestris; then the 



Periwinkle. 



