ISOPODA LIBERATICA, II. 357 
ISOPODA LIBERATICA.—Sub-tribe II. 
THE animals comprising the second sub-tribe of the 
Isopoda Liberatica (which is equivalent with the family 
Idoteides of M. Milne Edwards) differ from the general 
form of the order in the greater elongation and _ paral- 
lelism of the body, which is more or less abruptly trun- 
cated at each extremity. In the most extreme forms 
the body is quite cylindrical, resembling that of the 
larvee of certain Lepidopterous insects (Geometra), even 
in its peculiar movements and position when at. rest. 
The eyes are large and lateral, the anterior pair of an- 
tenne are very short, and inserted above the posterior 
pair, which are considerably—oceasionally very much— 
elongated. . The mandibles are short, robust, and horny, 
with a strong denticulated apical incurved tooth, below 
which, on the inner margin, is a smaller denticulated and 
movable tooth: these organs are destitute of a palpiform 
appendage. The outer foot-jaws have the second joint 
produced into an elongated plate, ciliated at the tip with 
a hook in the middle of its interior margin; the four 
_ terminal joints are variable in size, the fourth in Jdotea 
being large and oval, whilst it is very small in Arcturus. 
The legs vary both in size and arrangement, the four 
anterior pairs in Arcturus being very slender, ciliated, and 
directed forwards, whilst the three posterior pairs are 
short and very robust, and directed backwards ; whilst in 
Idotea the legs are nearly of equal size and character, the 
three anterior pairs being directed forwards, and the four 
