LvEMODIPODA. 315 



and inferior extremity. The feet are terminated by a stout hook. 

 The four anterior, the second of which are the largest, are always 

 terminated by a monodactyle forceps or a claw. In several, the 

 four following ones are shortened, less articulated, without the ter- 

 minal hook, or are rudiraental, and nowise adapted for the ordinary 

 uses of similar parts. 



The females carry their ova under the second and third segments 

 of the body, in a pouch formed of approximated scales. They are 

 all marine Crustacea. 



We may unite them in a single genus which, by the law of priority, 

 should be called 



Cyamus, Lat. 

 Now divided into Leptomera, Naupredia, Caprella, and Cyamus proper. 



ORDER V. 



ISOPODA.(l) 



The Isopoda approach the Lsemodipoda by the absence of the 

 palpi of the mandibles, but are removed from them in several other 

 respects. The two anterior feet are not attached to the head, and 

 belong, as well as the following ones, to a particular segment. 

 They are always fourteen in number, unguiculated, and without any 

 vesicular appendage at their base. The under part of the tail is 

 furnished with very apparent appendages resembling leaflets or vesi- 

 cular bursae, the two first or external of which, either partially or 

 wholly, usually cover the others. The body is generally flattened, 

 or is wider than it is thick. The mouth consists of the same pieces 

 as in the preceding Crustacea; but here, those which correspond 

 to the two superior foot-jaws of the Decapoda, exhibit an appear- 

 ance of a lower lip terminated by two palpi, still more than in the 

 latter. The two mediate antennae are almost obliterated in the last 

 Crustacea of this order, which are all terrestrial, and also differ from 

 the others in their respiratory apparatus. Most of them are aqua- 



(1) Equal-footed. 



