232 
HISTORY OF BRITISH CRUSTACEA. 
gression ; when pursued along the bottom, it runs quickly, 
but often stops suddenly, turns round, and becomes assailant. 
Gen. 116. ONI8CODA, Latr. 
Caudal appendages long. Front legs largest; claws 
bifid. Eyes moderate, somewhat vertical ; antennae four; 
the lower shorter than the bristle-bearing joint of the outer 
pair. 
Oniscoda maculosa, Leach. Spotted Hog -louse. (Plate 
XII. fig. 7.) — Body ash-coloured, varied and spotted with 
brown. 
In the sea, among Algae. 
Fam. ONISGIDJS. 
The species of this family appear to have only one pair of 
antennae ; the other pair being in a rudimentary state. Ab- 
domen formed of six perfectly distinct segments ; the last 
of these does not acquire the dimensions which it exhibits 
in the other Isopoda , where it serves as a shield to the false 
branchial feet ; it is, on the contrary, very small, and some- 
times even rudimentary. Their legs are slender. 
The species of Oniscidce are not so aquatic as the other 
