140 
HISTORY OF BRITISH CRUSTACEA. 
being composed of plates or of simple filaments, are com- 
posed of cylinders arranged parallelly, from which arise 
other smaller cylinders, and these in their turn are also 
ciliated. There are seven, and in some cases eight, pairs of 
legs ; and as they are often near the mouth, the name of the 
Order has been derived from this circumstance.^ There are 
generally six pairs of abdominal appendages. 
Species of three families of this Order have been found 
on our coasts, but those belonging to the families Squillidm 
and Phyllosomada can scarcely be regarded as indigenous. 
Some of the exotic species of Squilla are very large and 
striking, while the transparent Phyllosomata and curiously 
spined glassy Erichthus and Alima are among the most 
wonderful of all the Crustacea. The species of the family 
Mysididce are often very abundant, and in some parts of 
the world are important to man. One species, My sis 
fiexuosuSy is thus referred to by Sir James Clark Ross;f 
“ It inhabits some parts of the Arctic Ocean in amazing 
numbers, and constitutes the principal food of the pro- 
digious shoals of Salmon that resort thither in the months 
of July and August, and upon which the inhabitants of 
* 2 Toixa , a mouth ; and irovs , tto^os, a foot. 
f Appendix to Ross’s Second Voyage, p. 85. 
