ARCTURUS. 361 
ISOPODA. ARCTURID. 
NORMALIA. 
Genus—ARCTURUS. (Latreille.) 
Leacia. JonnsTon, Edinb. Phil. Journ. xiii. 219 (1825). Wxstwoop 
(subg.). 
Astacilla, Furmine. 
Leachia. Mtuxu Epwarps (subg.). H. Goopstr. 
Tue 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 antenne 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 
