BnANCHIOPODA, 
239 
antenna?. Their feet, with a few exceptions, are wholly natatory. 
Their number varies, being but six in some, while in others it 
amounts to twenty, forty-two, or more than a hundred. Many of 
them have but one eye. 
Most of these animals, as we have already stated, being nearly 
microscopical, it is evident that the application of one of the charac- 
ters we have employed — that of the presence or absence of the palpi 
of the mandibles' — with respect to them, presents almost insuperable 
difficulties * . The form and number of the feet, that of the eyes, 
the shell, the antennce, furnish us with more visible marks, and such 
as are within the observtion of every one. 
This order in the systems of De Geer, Fabricius and Linnaeus, a 
single species excepted — M. polyphemiis, contained by a single genus 
Monoculus, Lin.\ 
Which we will divide into two principal sections. 
The first, — that of the Lophyropa — is distinguished by the number 
of feet, which never extends beyond ten ; their joints are also more 
or less cylindrical or conical, and never entirely lamelliform or foli- 
aceous ; the branchiae are but few in number, and most of them have 
but one eye. Several besides, have mandibles provided with a pal- 
pus J ; there are, almost always, four antennae which serve for loco- 
motion. 
In the second section — that of the Phyllopa — the number of feet 
is increased to at least twenty, and in some amounts to many more ; 
their joints, or at least the last ones, are flattened and resemble cili- 
ted leaflets. The palpi of the mandibles are always wanting. They 
all have two eyes, situated in some at the extremity of two moveable 
pedicles; their antennae, but two in number in several, are generally 
small and not fitted for natation. 
We will divide the Lophyropa into three principal and very natural 
groups, the two first of which approach the Crustacea of our three 
first orders in their mandibles, each of which is furnished with a 
palpus, and in some other characters. 
1. Those Carcinoida, Lat. — whose more or less ovoid shell is not 
doubled like that of a bivalve, and leaves the inferior portion of the 
body exposed. They never have antennae resembling ramified arms 
They have ten feet, more or less cylindrical or setaceous. I’lie ova, 
in those females whose gestation has been observed, are contained in 
two external sacs situated at the base of their tail. Some of them 
have eyes. 
* We will begin, however, with those llranchiopoda whose mandibles are furnished, 
with palpi ; they constitute the two first divisions of the Lophyropa. 
't- And that of Binode in the system of Geoffroy. 
J M. Straus appears to attribute tliis character exclusively to Cypris and Cythe- 
rea, which compose his order of the Ostrapoda ; but from the observations of Juriue, 
Sen., and RanUobi-, it seems that it also belongs to Cyclops. 
