ISOPODA. 209 
Division—AQUAS PIRANTIA. 
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—Bopyride. 
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 antennz concealed 
beneath the porrected front of the head. Family— 
Cymothoide (of which no representative has hitherto 
been recorded as a native of our coasts). 
B. Those which have the antenne naked or but slightly 
covered at the base. Family—Hgide. 
VOL. II. 12 
