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 tip; the mouth placed in the ordinary 
situation, and composed of a labrum, a lingua, a tongue, two mandibles, often palpi- 
geroust, 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 ; 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 a coquille) of Muller, 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 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 
I siphon itself being either internal, or the action of suction being performed by a kind 
I of sucking cup (ventouse). 
1 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 
1 edition of this book, I had considered as a section of the preceding order. 
jt * Jurine divided the class into two sections, founded upon the pre- 
i! sence or want of jaws, in his Memoir on Argulus. [Latreille also 
|l adopted this as a primary character in his Cours d’ Entomologie.'] 
I t The four anterior, when there are fourteen, are formed of the 
I four posterior foot-jaws. In the Decapoda the six foot-jaws are ap- 
j plied to the mouth, and serve as under-jaws. 
i] t [This peculiarity never occurs in the true insects, and serves to 
ij prove that the mandibles are but modified maxillse, or rather, to speak 
[ more theoretically, the inferior appendages of one of the articulations 
j of the body.] 
I § In my Families Naturelles du Rigne Animal, the Entomostraca 
,| were divided into four orders, namely, Lophyropoda, Phyllopoda, 
I Xiphosura, and Siphonostoma. [The Entomostracous Crustacea, like 
I the Invertebrata, having 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 
1 a greater number of orders and primary groups for their reception 
I 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 d’Entomologie subsequently 
published. Milne Edwards, Burmeister, and De Haan have especially 
investigated these animals during the last ten years, and it will be 
i serviceable to give a short abstract of the arrangements which they 
have proposed, especially as the works of the two last-named authors 
I are in the hands of so few naturalists, that even Milne Edwards has 
I I not mentioned them in his Review of Crustaceology (Suites de Buffon ) . 
j Latreille himself, in his Co?jrs d’Entomologie, had cut up the Ento- 
I I niOstrdC& (which he h&d 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 (Suites de Buffon, Crust. I. p. 236, 
modified from that published in the Annales des Sci. Nat., March, 
1830). 
Subclass I. — Crustacea with maxillse. 
Legion 1. Podoplhalma. 
Order 1. Decapoda. 
2. Stomapoda. 
Legion 2. Edriopthalma. 
Orders. Amphipoda. 
Order 4. Isopoda Order 5. Loemipoda. 
Legion 2. Branchiopoda, Legion 3. Entomostraca. 
Order 6. Ostrapoda (Cythere). Order 8. Copepoda (Cyclops) . 
7. Phyllopoda. 9. Cladocera(Daphnia,&c.) 
Legion 4. Trilobita. 
Subclass II. — Crustacea with a sucker. 
Legion I. Ambulatory Parasites. 
Order 10. Araneiformes (Pycnogonum). 
Legion 2. Swimming Parasites. 
Order 11. Siphonostoma. 
12. Lerne®. 
Subclass III. — Crustacea Xiphosura. 
Order 13. Xiphosura. 
Burmeister, in his Grundriss fur Naturgeschichte, Zoologischer 
I Handatlas, and Memoir on the Cirripedes, has divided the class into 
three orders only 
