ISOPODA. 209 



Division AQUAS FIR ANTI A. 



THE animals composing this division are likewise 

 divisible into two tribes, according to the nature of 

 their habits and the situations in which they are conse- 

 quently found, being either 1. Parasitica, parasitic and 

 fixed on other aquatic animals, or, 2. Liberatica, free, 

 and crawling or swimming about in the water. 



Tribe PARASITICA. 



The first of these tribes comprises the species which 

 reside upon other crustaceans and fishes, and which may 

 conveniently be subdivided in the following manner : 



1. Those in which the sexes are greatly dissimilar in 

 form and size, and which are parasitic upon other crus- 

 taceous animals. Family Bopyridce. 



2. Those in which the sexes are similar in general 

 form and size, which are found parasitic upon fishes, and 

 which are divisible into 



A. Those which have the base of the antennae concealed 

 beneath the porrected front of the head. Family 



Cymothoida (of which no representative has hitherto 

 been recorded as a native of our coasts). 



B. Those which have the antennaa naked or but slightly 

 covered at the base. Family Mgidcs. 



VOL. IT. 



