192 CLASS CRUSTACEA. 



ceding articulation annulated; this character is proper to the 

 other foot only at the first of these articulations ; the feet of the 

 fourth pair are longer than the preceding and the two following; 

 the upper antennae have but two threads. {Nika edulis, Risso,) 



Hymenocera, Lair., 



Have the two anterior feet terminated by a long hook, bifid 

 at the end, and with very short divisions ; the two following 

 are very large : the hands, the fixed finger, and the upper 

 thread of the middle antennse are dilated, membranaceous, 

 and, as it were, foliaceous ; the external jaw-feet are likewise 

 foliaceous, and cover the mouth. 



We shall now pass to some subgenera in which the claws 

 present no remarkable or unusual particularity. 



Sometimes the upper or middle antennse are terminated but 

 by two threads ; the bill is generally short. 



Gnathophyllum, Lair., 



The only ones, which, in the relation of the form and amplitude 

 of the lower jaw-feet, approach hymenocera; the four anterior 

 feet are in the form of didactylous claws ; the second pair is 

 longer and thicker than the first ; none of the articulations of 

 the four ai'e annulated. {Alpheiis elegans, Risso.) 



Pontonia, Lair., 



Have, like the two following subgenera, the four anterior feet 

 in the form of claws, and didactylous, but the carpus is not an- 

 nulated. [Alpheus thyrenus, Risso.) 



Alpheus, Fah., 



Which have also the four anterior feet terminated by a 

 didactylous forceps, but the carpus of the second is articu- 

 lated ; these last are shorter than the first. {Alpheus mala- 

 baricus, Fab.) 



