120 CRUSTACEA. 



mined. Two of the antennae (chelicera Latr.) arc in general 

 cheliform, and perform the office of pincers. They are gene- 

 rally parasites, living upon the bodies of other aquatic animals, 

 especially fishes. 



This order comprises two principal sections or sub-orders : 



1. Xyphosura (Latreille), in which the carapax is bipartite, 

 the suctorial apparatus wanting, and its place supplied by the 

 dilated bases of the forelegs. The type of this section is 

 the genus JAmulus (Fabricius), the species of which are 

 known by the common name of king crabs, having the body 

 covered by a large and nearly rounded shell, divided into two 

 parts, the anterior being large and semilunar, and the poste- 

 rior toothed at the sides, and deeply notched behind, and ter- 

 minated by a very long and acute spine ; the mouth is not 

 provided with any sucker, the coxae of the six anterior pairs 

 of legs being dilated and spined, and performing the office of 

 jaws. These king crabs sometimes attain the length of two 

 or three feet. They inhabit the tropical seas, frequenting the 

 coasts, and appearing to be found only in the East Indies and 

 the shores of America. According to M. Leconte, they are 

 given to pigs for food, and the long and pointed tail is some- 

 times employed by the Indians for the points of their arrows. 

 Their eggs are eaten by the Chinese. 



2. Siphonostomata (Latreille), in which the mouth is 

 evidently more or less suctorial, and the carapax composed 

 of a single piece. It comprises the two families Caligidee and 

 Dichelestionidee. 



In the parasitic family Caligidee, the body is covered by 

 an oval or semilunar transparent shield, flattened above, \vith 

 twelve legs, the four last pairs of which are feathered and 

 pinnate, being admirably formed for swimming. The tail is 

 more or less elongated and exposed, and terminated by two 

 appendages. The genus Argulus is established for the recep- 

 tion of a small but very curious (British) animal found upon 



