43G CRUSTACEA. 



R'eqiie AiihiuiL altliuu;;'h Latreille liimself, as stated in p. 410, in his more recent Ti'ork, 

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



THE FIRST ORDER OF ENTOMOSTRACA — 



(Ths Sixth of tlte Class Crustacea), — 



BRANCHIOrODA,- 



Has, for its characters, a month composed of an upper hp, two mandibk'S, a tongue, 

 and one or two pairs f)f maxilla"' ; and the biancliirc, or the first of these organs when 

 there are man)', always anterior. 



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

 form of a shield, or bivalve case, and provided with two or fjur antenna^. The legs, 

 except in a few, are only fitted for swimming: they are varialile 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 e)'es, the shell and the antennis, 

 v.dll furnish characters of more ready application, and capable of being examined b)^ 

 every inf|uirer. 



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

 Linnaais [with the exception of a single species, M. pohjphoinis'], the single genus, 



MoNoeULus (Linn.).t — 

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

 subsections, Carciimiiln, Ostracothi. and C/ndorrra ; and, '2. Puyllopa, divisible into 

 two subsections, CenilnptlKihiKi and Aspiiliphoni. 



The fir.st section of tlie BrfinrliiniirHin — that of the LopriYROPA — is distinguished by 

 the number of the legs, which never exceeds ten, and of which the joints are c\ lindrical or 

 couical, and never entirely lauicllifiirm or foliacenus. The liranchia' arc few in number, and 

 the majority have imh' one eye. ^huiy, also, have tlie mandibles famished with a palpus. 

 The antenna; are generally four in number, and are used in locomotion. + 



We divide the Lo])hyr(Jiia into three principal and very natural divisions, and of which the 

 two tirst agree with the preceding Crustacea m their ])alpigerons mandibles, and some other 

 characters. 



The first division of tlic Lopliyropoiis lliiuichiopoda, or tliat of the C.vrcinoida, Latr., lias the shell 

 more ()r less nviiid, or o\;il, iint shutting in t\\o parts in the manner of a bivalve shell, hut le;iving the 

 loner part of the boily naked. Their antennae have never the appearance of branching arms. The legs 

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

 tion has Ijocii 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 tirst subdivision. 



Tliose species which have the thorax entirely covered by the shell, wilh the eyes large, and the inter- 

 mediate auteiuKe terminated by two (ilanients, compose the two following genera. 



• We ueverlhclcss arrnngc. nt tlic head, nil Uinsc Iirriiic]iiL>,,„(hi 1 StrrLiiBs uppe.irs to al Iribvitc this charncior exclusively tu Cyrrig 



ulilch haye the mandibles funiislied iviih pal|,i. I'hey eoinpose the ami Cytliere; but from the olisetvatioiis .il the ehler Jurine and 



*,wo first tlivisioiis of the Lophyropa. j Itumdohr, it exists alsii in Cyelops. 



t Together with that of Binoeulus of OcolTroy. 



