2 
HISTORY OF BRITISH CRUSTACEA. 
retail them by the dozen. These are the chief Crustacea 
eaten in London, exclusive of thousands of the Shore Crab, 
which may be seen, by the side of Whelks and Periwinkles, 
on stalls in the poorer neighbourhoods, where they find ready 
purchasers in many a ragged gourmand . 
The great Craw-fish, or Thorny Lobster, and a limited 
number of the small fresh-water Cray-fish — in all, some 
eight or ten species of Crustacea — exhaust the list of the 
members of this class of animals, sold as food in our Metro- 
polis. Although Crustacea directly do not greatly add to 
our supplies of food, yet they indirectly assist very mate- 
rially in contributing to our wants. The great mass of fish 
derive their principal food from the smaller members of this 
class, which swarm in our seas by myriads ; and, in this w T ay, 
Crustacea contribute greatly to our comfort. They are the 
nutritious food not only of vast shoals of fish, but of sw T arms 
of sea-birds, some of which feed almost exclusively on them, 
particularly in the Arctic parts of the ocean. Crustacea also 
form the bulk of the food which supports the vast bodies of 
the Whale tribe, as may be seen somewhat further on, under 
the description of the Mysidida, one of the families of the 
order Stomapoda. The small terrestrial species, — such, for 
instance, as the little Hog-lice of the genera Oniscus and 
