ARCTURID^. 359 



Family ARCTURID^. 



THIS family, corresponding with the tribe Idoteides 

 Arpenteuses of M. Milne Edwards, is composed of the 

 single genus Arcturus, of Latreille, remarkable amongst 

 the Isopoda for its slender, cylindrical form, the length 

 of its lower pair of antennae, and the delicate ciliated 

 structure of the four anterior pairs of legs ; whilst the 

 hind ones are short and very robust. In the British 

 species, the fourth segment of the body is greatly elon- 

 gated, and as the animals affix themselves by means of 

 their hind pairs of legs, elevating the front part of the 

 body, and twisting it about in various directions, they 

 exhibit considerable resemblance to the Caprella, as also 

 to the loopers, or Geometrical Caterpillars of the Geo- 

 metry , whilst the elongated antennas give them also a 

 strong resemblance to the Amphipodans, constituting the 

 genus Corophium (vol. i p. 493) ; in fact it is by the assist- 

 ance of the great antennae that these creatures chiefly 

 progress, their fore legs being too delicate to serve as 

 instruments of locomotion. 



The species of the group found in the Arctic seas 

 are of very large size, sometimes reaching three inches 

 in the length of their bodies. This is the case with the 

 type of the genus Idotea Bqffini, Sabine, first described 

 in the appendix to Captain Parry's fourth voyage. This 

 species has the fourth joint of the body not much longer 

 than the adjoining segments, and if it should be con- 

 sidered necessary to separate the British species, as form- 



