CHAE DE Ry Vall 
REMARKS ON THE DISTRIBUTION OF MARINE AND FRESH-WATER 
CRUSTACEA 
A. Marine. 
THE great majority of the Crustacea are inhabitants of the 
sea. From a Zoogeographical point of view we divide the sea 
into three chief regions, each of which is characterised by 
a special kind of fauna—the littoral, the pelagic, and the 
abyssal regions. 
The littoral region, which comprises all the shallow coastal 
waters down to about 100 fathoms, varies very greatly in its 
physical character according to the nature of the coast, its 
geological constitution, latitude, ete., but, on the whole, it is 
characterised by variability of temperature and salinity, by the 
presence of sunlight, and by the continuous motion of its waves. 
On the shores of the large oceans this region is also greatly 
affected by the tides. It is mhabited by a vast assemblage of 
Crustacea, all of which are dependent upon a solid substratum, 
either of rock or sand, or of vegetable or animal growth, upon 
which they may wander in search of food, or in which they may 
hide themselves. In consequence, the character of the Crustacea 
on any shore is largely determined by its geological nature. 
Although a certain number of Entomostraca (such as Cope- 
poda (Harpacticidae and Cyclopidae), Ostracoda (Cypridae and 
Cytheridae), and a few Operculata are littoral in habit, it is the 
Malacostraca, from their larger size and variety of form, which 
give the character to coastal waters. 
On rocky coasts, especially those affected by tides, a great 
many kinds of Shore-crab are found, which hide at low tide in 
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