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 Squillidce 

 and Phi/llosomadce can scarcely be regarded as indigenous. 

 Some of the exotic species of Squilla are very large and 

 striking, while the transparent PhyUosomata and curiously 

 spined glassy Erichthas and Alima are among the most 

 wonderful of all the Crustacea. The species of the family 

 3fysidid<$ are often very abundant, and in some parts of 

 the world are important to man. One species, Mysis 

 flexuosus, 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 



* Sro^a, a mouth ; and ttovs, ttooos, a foot, 

 f Appendix to Ross's Second Voyage, p. 85. 



