BRANCHIOPODA. 301 



ORDER I. 



BRANCHIOPODA*. 



A MOUTH composed of a labrum, two mandibles, a ligula, and one or two 

 pairs of jaws, and branchiae, the first of 

 which, when there are several, are always 

 anterior, charactertise this order or the 

 sixth of the class. 



These Crustacea are always errant, and are generally protected by a shell 

 resembling that of a bivalve, and furnished with four or two antennae. 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 microscopal, 

 it is evident that the application of one of the characters 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 antennae, furnish us with more visible 

 marks, and such as are within the observation of every one. 



This order, in the systems of De Geer, Fabricius, and Linnaeus, a single 

 species excepted, M. Polyphemus, contained but the single genus 



MONOCULUS, Linnceus, 

 Which is now divided into two great sections and various subgenera. 



Gill-footed. 



