ORDER AMPHIPODA. 
205 
second jaw -feet, is always annexed to a particular segment, 
the first after the head. The antennae, whose number, with 
but a single exception ( phronima ) is four, are advanced, 
gradually become slender, terminating in a point, and are 
composed, as in the preceding Crustacea, of a peduncle, and 
of a single stem, or accompanied at most by a small lateral 
branch, and most frequently pluriarticulate. The body is 
usually compressed, and curved underneath posteriorly. The 
appendages of the end of the tail most frequently resemble 
small articulated stylets. These Crustacea may be comprized 
in a single genus, that of 
Gammarus, Fab., 
Which may be divided at first, according to the form and 
number of the feet, into three sections. 
1. Those which have fourteen feet, all terminated by a 
hook, or the same number terminating in a point. 
2. Those whose number of feet is also fourteen, but in 
which these organs, or the last four at least, are imperfect, 
and simply natatory. 
3. Those which have but ten apparent feet. 
The first section will be divided into two — 
The first, Uroptera, Latr ., have the head thick in gene- 
ral, the antennae often short, and simply two in number in 
some, and the body soft. All the feet, the fifth pair at most 
excepted, are simple. The anterior are short or small, and the 
tail is either accompanied at the end with lateral fins, or ter- 
minated by appendages or points, widened and bidenticulated, 
or forked at their posterior extremity. 
In some, as in 
Phronima, Latr. 
There are but two antennae, very short, and biarticulate. The 
fifth pair of feet is the largest of all, and terminated in a di- 
