CRUSTACEA. 



409 



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

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

 and ten or fourteen f legs, hooked at the ti}^ ; 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 : — 1 . Decapoda ; 2. Stomapoda ; 3 . Lcemodipoda ; 

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

 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 MoUusca. The eyes are ordinarily sessile, and often there is but one 

 of these organs. The legs, of which 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 clai<s into two sections, founded upon the pre- 

 sence or want of jaws, in his Memoir on Arj^lus. [Latreille also 

 adopted this as a primary character in his Coura d' Entomulogif ."] 



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

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

 plied to the mouth, and serve as under jaws. 



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

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

 more theoretically, the inferior appendages of one of the articulations 

 of the body.] 



5 In my Fiimillrs Nritmelh-s du R>g7ie Animnl, the Entomostraca 

 were divided into four orders, namely, Lophyropoda, Phyllopoda, 

 Xiphosura, and Siphonostoma. [The Entomostracous Crustacea, like 

 the Invertebrata, having been proved by recent investigators to con- 

 sist of several tribes of animals much more strongly modiBed i-n their 

 structure than the Malacostraca, it has become necessary to establish 

 a greater number of orders and primary groups for their reception 

 than were proposed in this work, and Latreille hi>nself became aware 

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

 arrangement of the class in his Coura d'Entmnnlogic subseciuently 

 published. Milne Edwards, Burmeister, and De Haau have espcci.iUy 

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

 serviceable to give a short abstract of the arrangements which tliey 

 have proposed, especially as 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 [Suitfs de Biiffou) . 

 I.ilreillo himself, in his ffur< d' Enttnnalogif, had cut up the Ento- 

 uwstraca (which he had sunk as a primary 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 following sketch I^Suites de Buffoti, Crust. I. p. 23(i, 

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

 1830). 



Subclass I. — Crustacea with nia.\illie. 

 Legion 1. Podopthalma. 

 Order 1 Decapoda. 

 2. Stomapoda. 

 Legion 2. Edriopthalma. 

 Orders. Amphipoda. 

 Order 4. Isopoda Order 5. Leemipoda. 



Legion 2. Branchiopoda. Legion 3. Kutomostraca. 



Order 6. Ostrapoda(Cylhcre). Order 8. Copepoda (Cyclops) . 



7. PhyUopoda. 9. Cladoccra(l)aphnia,&c.) 



Legion 4. Trilobita. 

 Subclass II. — Crustacea with a sucker. 

 Legion I. Ambulatory Parasites. 



Order 10. .'\raneifurmcs (Pycnogonum). 

 Legion 2. Swimming Parasites. 

 Order 11. Siphonostoma. 

 12. Leriieic. 



;n 111. — Crustacea Xiphosura. 

 Order 13. Xiphosura. 



Gruudriaa fur Naturgeachicbte^ Zootogiachrr 

 itidiitlna, and Memoir on the Cirripcdes, has divided the class into 

 iCe orders oiilv :— 



Subcia 



Burmeister, in hi: 



