BRANCHIOPODA. 239 



antennae. Their feet, with a few exception*, 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 those 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 

 ditlirultirs* . The form and number of the feet, that of the eyes. 

 the shell, the anti-nil*, 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. polyphemus, contained by a single genus 



MONOCULUS, 



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 

 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 

 v have ten feet, more or less cylindrical or setaceous. The 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 begjn, however, with those Branchiopoda whose mandibles are furnished 

 \\\\\\ palpi ; they constitute the two first divisions of the Lophyropa. 



f And that of Binocte in the system of Geoffrey. 



J M. Straus appears to attribute this character exclusively to Cypris and Cythe- 

 rea, which compose his order of the Ostrapoda ; but from the observations of Juxiuc, 

 . and RauUohr, it seems that it also belongs to Cyclops. 



