STOMAPODA. 313 



foot-jaws are transformed into feet, sometimes simple and at others 

 constituting a claw, but almost always with a single toe or hook. 



All these Crustacea are small, and mostly inhabit the sea-coast 

 or fresh water. Some are terrestrial, and others are known which 

 are parasitical. 



ORDER III. 



AMPHIPODA. 



The Amphipoda are the only Malacostraca with sessile and im- 

 movable eyes, whose mandibles, like those of the preceding Crus- 

 tacea, are furnished with a palpus, and the only ones whose sub- 

 caudal appendages, always very apparent, by their narrow and 

 elongated form, their articulations, bifurcations, and other incisures, 

 as well as by the hairs or cilia with which they are provided, resem- 

 ble false or natatory feet. In the Malacostraca of the following 

 orders, these appendages have the form of lamina? or scales; here 

 these hairs and cilia appear to constitute the branchiae. Many of 

 them, like the Stomapoda and the Losmodipoda, have vesicular burss 

 either between their feet or at their external base, the use of which 

 is unknown. 



The first pair of feet, or that which corresponds to the second 

 foot-jaws, is always annexed to a particular segment, the first after 

 the head. The antennas, which, with a single exception the Phro- 

 nirna3, are four in number, project, gradually taper into a point, 

 and consist, as in the preceding Crustacea, of a peduncle and a 

 single stem, or one furnished at most with a little lateral branch, and 

 usually composed of several joints. The body is generally com- 

 pressed and curved beneath posteriorly. The terminal appendages 

 of the tail are most frequently styliform and articulated. Most of 

 them swim and leap with facility and always laterally. Some in- 

 habit springs and rivulets; most of them however live in salt water. 

 Their colour is uniform, verging on reddish or greenish. 



They may all be comprised in a single genus, that of 

 2 P 



