ORDER BRANCHIOPODA. 
351 
the body is almost filiform, composed of a head separated 
from the trunk by a sort of neck ; of a trunk or thorax, 
hollow underneath, in its length, divided, at least above, the 
neck not comprized, into eleven segments, each supporting 
a pair of branchial feet, very much compressed, generally 
composed of three lamellate articulations, with the edges fur- 
nished with a fringe of hairs, or barbed filaments ; and of 
an elongated tail, going into a point, consisting of nine seg- 
ments, terminated by two leaflets, more or less elongated, and 
bordered with cilia). The under part of its second segment 
presents the male sexual organs, and in the female an elongated 
sac, containing the eggs which she is ready to lay. The 
head presents, first, two reticulated eyes, apart, situated at the 
extremity of two flexible peduncles, formed by lateral ex- 
tensions of the head. Second, two antennas, at the least, 
frontal, scarcely longer than the head, slender, filiform, and 
composed of very small articulations. Third, two projections 
underneath these antennae, sometimes in the form of horns, and 
having a single articulation, sometimes digitiform, (the first 
finger of the hands, according to Prevost) and of two articula- 
tions. Fourth, a lower mouth, composed of two sorts of den- 
ticulated mandibles, without palpi, and of some other pieces. 
We presume that these projections in the form of horns, are 
only an appendage, or division of the frontal antenna?, but in- 
creased in size and altered in shape in the males. The two other 
antenna) may be wanting or obliterated in the females, and form 
in the other sex of one of the species ( Chirocephale diaphane , 
Prevost), those singular tentacula, appcndaged, and denticu- 
lated, in the form of a flabby proboscis, capable of being spirally 
rolled, which Benedict Prevost designates under the name of 
fingers of the hands. It is probable that the mouth has, as in 
apus, two pairs ofjaws,a ligula, and a labrum,but the forms and 
respective situations of which have not yet been well recog- 
nized. It appears to me indubitable, that this piece, in the 
