Cvi INTRODUCTION. [CH. 



The second zone is called the Laminarian, from the 

 belt of that kind of seaweed which girds all the rocky 

 parts of our coast-line. It is seldom laid bare^ except at 

 very low spring-tides ; and it is generally much narrower 

 than the littoral zone, in consequence of the rocks, to 

 which the Laminaria or tangle is attached, dipping sea- 

 ward and being covered with sand beyond the direct and 

 more immediate influence of the tide. This zone may 

 be said to extend from low- water mark to 10 fathoms. 

 The mollusca which inhabit it chiefly belong to Patella, 

 Acmcea, Trochus, Lacuna, Rissoa, and Jeffreysia, all of 

 which are phytophagous or vegetable-eaters, as well as 

 the Nudibranchs or sea-slugs, which are mostly zoopha- 

 gous. Where the coast is sandy, this zone is entirely 

 wanting and is merged into the one above or below it, 

 so far as regards its zoological contents. The extent of 

 each zone mainly depends on its capability as a feeding- 

 ground; and the same species are frequently common 

 to every zone, when their nature is alike and they are 

 not prevented by an intervening barrier of sand or rock 

 from spreading from one zone to another. To this cause 

 is probably owing the great variation in the depth to 

 which many species attain. The common mussel, which 

 is usually found within tide-marks, has been recorded by 

 Dr. Walker as living in the North Sea at a depth of 

 140 fathoms or 840 feet. Cyprina Islandica, which in 

 most seas inhabits depths of from 30 to 140 fathoms, 

 occurs on the coast of South Wales at low- water mark ; 

 and our little cowry {CyprcBa Europcea) has a range from 

 low-water mark to 100 fathoms. 



The third zone has received the name of ^^ Coralline,^' 

 from the quantity of nullipore [Melobesia polymorpha) , 

 which is a stony coral-like plant, and in many places 

 covers large tracts of the sea-bed. Its width varies con- 



