138 CRUSTACEA. 



Antkura (Leach). Feet clawed; four leaf-like 

 plates beneath the abdomen, which are prolonged 

 on each side on the dorsal surface of the last 

 segment. 



A. gracilis. Fig. 248 ; mag. \ . 

 cylindrica. 



Arcturus (Westwood). First four pairs of feet 

 armed with swimming-plates; the rest clawed; 

 antennae foot-like. 



A. longicornis. Fig. 249 ; n. s. 

 intermedius. 

 gracilis. 



Sub- Order III. AMPHIPODA. 



Fourth and fifth abdominal seg- 

 ments united ; fourth and fifth ab- 

 dominal appendages dissimilar . . Cheluracea. 



Abdominal segments distinct; 

 abdominal appendages similar : 



Foot-jaws covering only the bases 

 of the preceding appendages, and 

 forming a lip with three plates, but 

 deprived of palps Hyperiacea. 



Foot-jaws very large, covering 

 the whole mouth, and forming a 

 lip terminated by four great horny 

 plates and two very long palps . . Gammaracea. 



TRIBE I. CHELURACEA. 



Chelura (Philippi). First three segments of 

 abdomen carrying swimming feet ; the remainder 

 supporting a pair of leaf-like appendages and a 

 pair of cylindrical false feet, and terminated by 

 two leaping organs. Bores in submerged timber. 

 C. terebrans. Fig. 250 ; mag. f . 



