ZONES OF MARINE LIFE. 411 
barnacles, often striping the 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 Ly yuyu I 
a nullipore, forming a. hard pale fawepes: 
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 aiti- 
culatus, with its graceful even-edged rich brown fronds, mingled 
occasionally with the less elegant Fucus nodosus. Here limpets 
throng, and dog-periwinkles (Purpura lapillus) 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 Littorina littorea, gathered in thousands for 
the London market. On our western coasts 
we find it in company with the purple-striped 
top-shell (Zrechus 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 Penile. 
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 Laurencia pinnati- 
fida wppermost; then the green Conferva rupestris; then the 
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