CRUSTACEA. 



409 



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



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 ; S.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 ct 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 

 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 Pcecilopoda§, which, in the first 

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



* Jurine divided the class into two sections, founded upon the pre- 

 tence or want of jaws, in his Memoir on Argulus. [Latreille also 

 adopted this a* a primary iharacter in his tours d'Bntinnologle,] 



t The four anterior, when there art fourteen, are formed, 'if the 

 four posterior foot* Jaws, En the Decapod* the six foot-jaws are ap- 

 plied to tbfl mouth, and serve as under jaws. 



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

 prove that the inandiblcs are but . , ->r r.ihi r, in *p< ak 



more theoretically, the inferior appendages of one of the articulations 

 of the body.] 



$ In my Fnnillri NatUTtltet dn Rtgne Animal, the Kntomostraca 

 were divided Into four orders, namelr, Lopbrropoda, Phyllopoda, 

 Xiphosnra, and Blphonostome. [The Bntomostracous Crustacea, like 

 it*, baring d by recent investigators to con- 



skit of several tribes nl animal a much more strongly modified In tbeii 

 structure than the Malacotti ice, u bai become li- 

 ft greater number of order* 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 bis Cbstri d*&tttomologi* subsequently 

 published. MUnc BdwardSj Darmelster, and De II -inn have especially 

 gated these animals during the last ten yi irs, and It will be 

 serviceable to give a short abstract of the arrangements which they 

 have pi as the vorks o! the two last-named authors 



are in the hands "t so few naturalists, that ercn Miln- 

 not mentioned them in his Review of Crustac* 



• . bad i ut up the Kiit" 

 roost ram (which he had sunk as a primary section of the class In 



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

 Lopbrropoda, Ostrapoda, Phyllopoda, Xiphosura, and Slphonostoma, 

 and bad characterized several sub-orders which Kd wards subsequently 

 adopted in the following sketch [Sut.'ri dr Iluffuu, OttSt. I. | 

 modified from that published in the AnnaUs det 8ci. Sat., M 

 1830). 



Subclass I. — Crustacea with maxillts. 

 i 1. Pod opi halm*. 

 Order 1 I (ecapoda. 

 ■_' Rtomapode* 

 Legion 2. Bdrioptbalma, 

 Urder 3. Amphipoda, 

 Order 4. Isopoda Order 5. Lmmipoda. 



Legion 2. Branchiopoda. I traca. 



Order fi. Ostrapoda (Cy there). Order s, Copepoda I 



7. Phyllopoda. 9. l.'ladocera(l>aphm*,Sic.) 



Legion 4. Trilobita. 

 bus ii Crustacea with a sucker* 

 I gion i- Ambulatory Parasites. 



Order 10. .\t mi Iformei (Pycnogonom). 

 I i l,' I' tritsiies. 



Order 11. BIphonostonuL 



Subclass in - Crustacea TClphosura. 

 Ord < t t\ 



Buxmelster, In bis OrumdrU \te t Z oe- f os, 



H'tnititlat, and Memoir on the i Irrlpedes, has divided the tUsslnto 

 three orders only ;— 



