ISOPODA LIBERATICA, U. 357 



ISOPODA LIBERATICA.— Sub-tribe 11. 



The animals comprising the second sub-tribe of the 

 Isopoda Libei-atica (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 

 larvae 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- 

 tennae are very short, and inserted above the posterior 

 pair, which are considerably — occasionally 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 Idotea 

 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 



