Class 1. 



CRUSTACEA. 



409 



We divide the class into two sections, Malarostraca and Entomostraca.* 



The Malacostraca have the envelope ordinarily very solid, of a calcareous nature, 

 and ten or fourteen f legs, hooked at the tip; the mouth placed in the ordinary 

 situation, and composed of a labrum, a lingua, a tongue, two mandibles, often palpi- 

 gerousj, two pairs of maxillae covered by the foot-jaws. In a great number each of 

 the eyes is supported upon a moveable footstalk, articulated [at its base], and the 

 branchiae are hidden beneath the lateral margins of the carapax or shell ; in others, how- 

 ever, they are attached beneath the post-abdomen. 



The Malacostraca consist of five orders : — l.Decapoda; 2.Stomapoda ; Z.Lcemodipoda; 

 4. Amphipoda ; 5, Isopoda. The first four of these orders were included in the Linnaean 

 genus Cancer^ and the last in his genus Oniscus. 



The Entomostraca, or shell insects (insectes d, coquille) of MuUer, are composed of 

 the genus Monoculus of Linnaeus. The envelope is corneous, very slender, and the 

 body in the majority is covered by a shell, composed of two pieces, not unlike that of 

 the bivalve Mollusca. The eyes are ordinarily sessile, and often there is but one 

 of these organs. The legs, of w^hich the number varies, are, in the majority, 

 fitted only for swimming, without any terminal hook. Some of them are most 

 nearly allied to the preceding groups by having the mouth anteriorly situated, and 

 composed of a labrum, two mandibles (rarely palpigerous), a tongue, and at most two 

 pair of maxillae, the outer ones not being covered by foot-jaws. In the others, which 

 appear to approach the Arachnida in many respects, the organs of mastication some- 

 times merely consist of the coxae of the legs advanced and lobe-like, armed with 

 numerous small spines, and surrounding a large central pharynx : whilst in others they 

 form a small siphon or beak, used as a sucker, as in many Arachnida and Insects ; and 

 even sometimes they are not, or scarcely, visible on the exterior of the body, the 

 siphon itself being either internal, or the action of suction being performed by a kind 

 of sucking cup {ventouse). 



Hence the Entomostraca are either dentate or edentate. The dentate species com- 

 pose one order, Branchiopoda, and the edentate that of Poecilopoda§, which, in the first 

 edition of this book, I had considered as a section of the preceding order. 



• Jurine divided the cla-s into two sections, founded upon the pre- 

 lence or want of jaws, in his Memoir on Ar^ulus. [Latreille also 

 adnptcd this as a primary t haracter in his Conn dEntutnologie.] 



t The four anterior, when there art fourteen, are formed of the 

 four posterior foot jaws. In the Detapoda the six foot-jaws are ap- 

 plied to the month, and ser\'e as under jaws. 



J [This peculiarity never occurs in the true insects, and serves to 

 prove tliat the mandibles are but modified maxillae, or rather, to speak 

 more theoretically, the inferior appeudai^es of one of the articulations 

 ef the body.] 



§ In my Famillei NnturfUet du R>gne Animal^ the Entomostraca 

 «-ere di\ided into four orders, namely, Lophyropoda, Phyllopoda, 

 Xiphosura, and Siphonostoma. [The Entomostracous Crustacea, like 

 the Invertebraia. havinij been proved by recent investigators to con- 

 sist of several tribes of animals much more strongly modified in their 

 structure than the Malacostraca, it has become necessary to establish 

 ft greater number of orders and primary groups for their reception 

 than were proposed in this work, and Latreille himself became aware 

 of the necessity for such a step, having considerably altered the 

 arrangement of the class in his Cours dEntotnologie subsequently 

 published. Milne Edwards, Bunueister, and De Haan have especially 

 investigated these animals during the last ten years, and it will be 

 servictablc to give a short abstract of the arrangements which they 

 have proposed, especially hs the works of the two last-named authors 

 are in the hands of so few naturalists, that even Milne Edwards has 

 not mentioned them in his Review of Crustaceology {Suites de Bnffon) . 

 Latreille himself, in his CoKrj d'Entutnologir, had cut up the Ento- 

 awitraca (which he had sunk as a primar}- section of the class in 



favour of sections characterized by the mouth organs) into five orders, 

 Lophyropoda, Ostrapoda, Phyllopoda, Xiphosura, and Siphonostoma, 

 and had characterized several sub-orders which Edwards subsequently 

 adopted in the fnlluwitig sketch {Suites de Bnffon, Crust. I. p. 236, 

 modified from that published in the Annalts des Set. Nat., March, 



1830). 



Subclass f. — Crustacea \xith maxillse. 

 Legion 1. Podopthalma. 

 Order 1 Dccapoda. 

 2. Stomapoda, 

 Legion 2. Edriopihatma. 

 Order 3. Amphipoda. 

 Order 4. Isopoda Order 5. L(Emipoda. 



Legion 2. Branchiopoda. Legion 3. Kntomostraca. 



Order 6. Oslrapoda(Cythere). Order 8. Copepo'la (Cyclops). 



7- Phyllopoda. 9. Cladocera(l)aphtiia,Stc-) 



Legion 4. Trilobita 

 SnbclasH II. — Crustacea with a sucker. 

 Legion 1. Ambulatory ParaNites. 



Order 10. Araneifonnes (Pycnogonum). 

 Legion 2. Swimming Parasites. 

 Order 11. Siphonostoma, 

 12. Lernese. 

 Subclass 111 — Crustacea Xiphosura. 

 Order 13. Xiphosura. 

 Burmeister, in his Grundriss fur Natttrgeschichtf, Zoologlschrt 

 \ H'indntlas, and Memoir ou the Cirripedes, has divided the class into 

 three orders oulj : — 



