ARCTURUS. 361 



ISOPODA. ARCTURID^E. 



NORMALIA. 



Genus ARCTURUS. (Latreille.) 



Leacia. JOHNSTON, Edinb. Phil. Journ. xiii. 219 (1825). WESTWOOD 



(subg.). 



Astacilla. FLEMING. 

 Leachia. MILNE EDWARDS (subg.). H. GOODSIB. 



THE chief characters of this genus have been already 

 detailed in our observations on the family, whilst those 

 of the British species, as forming a distinct subgenus 

 from the Arctic type, A. Baffini, are characterized by the 

 great elongation of the fourth segment of the body 

 (which we believe varies somewhat in degree according 

 to the sexes), and which, joined to the more slender 

 form of the animals, allow a much greater freedom of 

 movement to the front part of their bodies, enabling them 

 to hunt for their prey round a fixed spot without moving 

 from it. The eyes are large, semi-globose, and lateral, 

 with the anterior-lateral angles of the head produced 

 in a forward direction. The upper pair of antennae are 

 very short, and terminate in an obtuse-pointed, uni-jointed 

 flagellum, whilst the lower pair are very long, sometimes 

 longer than the entire body, and terminated, in the 

 typical species, by a multiarticulated flagellum ; but in 

 the British species the flagellum consists of only three 

 joints, closely united together, deflexed and incurved, the 

 terminal joint at the tip being formed so as to make a 

 strong point by which, when fixed in an advanced posi- 

 tion, the animal is able to pull itself forward. 



The anterior pair of legs, although partaking of the 



