436 



CRUSTACEA. 



Regne Animal, although Latreille himself, as stated in p. 410, in his more recent work, 

 had raised some of those groups, subsequently described, to the rank of orders.] 



THE FIRST ORDER OF ENTOMOSTRACA ,— 



(The Sixth of the Class Crustacea), — 



BRANCHIOPODA- 



Has, for its characters, a mouth composed of an upper lip, two mandibles, a tongue, 

 and one or two pairs of maxillae ; and the branchiae, or the first of these organs when 

 there are many, always anterior. 



These Crustacea are always wandering about, generally covered by a shell in the 

 form of a shield, or bivalve case, and provided with two or four antennae. The legs, 

 except in a few, are only fitted for swimming : they are variable in their numbers, there 

 being only six in some, but in others there are from twenty to forty-two, or even more 

 than a hundred. Many exhibit only one eye. 



These Crustacea being for the most part microscopical, it will be perceived that the 

 application of one of the characters of which we have made use — namely, that of the 

 presence or absence of mandibular palpi — will here present nearly insurmountable dif- 

 ficulties.* The form, and the number of the legs and eyes, the shell and the antennae, 

 will furnish characters of more ready application, and capable of being examined by 

 every inquirer. 



The order of Branchiopoda composed, in the methods of De Geer, Fabricius, and 

 Linnaeus [with the exception of a single species, M. Polyphemus'], the single genus, 



Monoculus (Linn.),t — 

 Which we separate into two principal sections: 1. Lophyropa, divisible into three 

 subsections, Carcinoida, Ostracoda, and Cladocera ; and, 2. Phyllopa, divisible into 

 two subsections, Ceratopthalma and Aspidiphora. 



The first section of the Branchiopoda — that of the Lophyropa — is distinguished by 

 the number of the legs, which never exceeds ten, and of which the joints are cylindrical or 

 conical, and never entirely lamelliform or foliaceous. The branchiae are few in number, and 

 the majority have only one eye. Many, also, have the mandibles furnished with a palpus. 

 The antennae are generally four in number, and are used in locomotion. J 



We divide the Lophyropa into three principal and very natural divisions, and of which the 

 two first agree with the preceding Crustacea in their palpigerous mandibles, and some other 

 characters. 



The first division of the Lophyropous Branchiopoda, or that of the Carcinoida, Latr., has the shell 

 more or less ovoid, or oval, not shutting in two parts in the maimer of a bivalve shell, but leaving the 

 lower part of the body naked. Their antenna? have never the appearance of branching arms. The legs 

 are ten in number, and more or less cylindrical, or setaceous. The females in those species whose gesta- 

 tion has been observed, carry their eggs in two external sacs situated at the base of the tail. Some of 

 them have two distinct eyes, and form a first subdivision. 



Those species which have the thorax entirely covered by the shell, with the eyes large, and the inter- 

 mediate antennae terminated by two filaments, compose the two following genera. 



* We nevertheless arrange, at the head, all those Branchiopoda J Strauss appears to attribute this character exclusively to Cypris 



which have the mandibles furnished with palpi. They compose the and Cythere ; but from the observations of the elder Jurine and 



two iirst divisions of the Lophyropa. 1 Uamdohr, it exists also in Cyclops. 



+ Together with that of Binoculus of Geoffroy. 



