CRUSTACEA. 



409 



We divide the class into two sections, Mala* ostraca 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 kibrum, a lingua, a tongue, two mandibles, often palpi- 

 gerous + , two pairs of maxill33 covered by the foot-jaws. In a great number each of 

 the eyes is supported upon a moveable footstalk, articulated [at its base], ;ind 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 ; ^.Stomapoda ; o.Lccmodipoda; 

 4. Ainphipoda ; 5. Isopodu. The first four of these orders were included in the Linneean 

 genus Cancer, and the last in his genus On'iscus. 



The Entomostraca, or shell insects (insectes a coqullle) of MuUer, are composed of 

 the genus Monoculus of Linn^us. 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. Tbe 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 tbem 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 maxilh"e, 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 coxse of the legs advanced and lobe-like, armed with 

 numerous small sjnnes, 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 

 sijjhon itself being either internal, or the action of snction being performed by a kind 

 of sucking cup (i^entouse). 



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

 pose one order, Branchiopoda, and the edentate that of P(3ecilopoda§, wbich, in the first 

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



•■ Jurine ilitided lIil' c]:i:~s into two scu-tiui-is, foundi-fl upon the pre- 

 sence or want of yiws, in liis Memoir on Ari,'iiliis. [Lutreilk- also 

 Qdn|jtc<l this as a primary ih«rrtcter in liis Cuiirs d'EntonnAo^ie.'] 



t 'I'he four fin ttrior, when there art fourteen, are formeil uf the 

 foiir |io:iterii)r foot jaws. In the Decaiiodu the six foot-jaws are ap- 

 plied to the iniiuth, and serve as under jaws. 



t [Tliva [jetuliarily never occurs in the true insects, and serves to 

 prove that the mandibles iire but modifii.il Jiiaxiliaj, or rather, to sptak 

 iiujie theoretieally, the iiiU-tior appeiniaj^'-ds of one uf the urticulatlons 

 of tlie body.] 



5 In my FamiUcs Naturi^Ues du Rigne Animal, the Entoniostracii 

 were divi.ied into four oriiers, namely, Lophyropuda, Phyllopoda, 

 Xiphosura, and Siphonosloma. [The Entoiiiostracous Crustacea, like 

 the Invertebrata, havini^ been proved by recent investi{,'ators to 

 fiist of several tribes r 

 structure than the Ma 

 umber of 



strongly inudjfied in their 

 itraca, it lias become necessary to establish 

 3rs and primary groups for their reception 

 i work, and Latreiile himself became aware 

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

 arraiigement of tbe class in his Coiirs d'Entmnulogie suhsequently 

 published. Milne Edwards, Burmeister, and De Haim have especially 



■eater i 



. were pn. 



erl these animals during the last 

 serviceable to give a short nbstract of the arrangements 

 have proposed, especially as the works of the two last-nam 

 are in the hands of so few naturalists, that even Milne E' 

 not mcntioneti them in his Review of Crustaeeology {Saltrs dc Bnjfoii). j 

 Latreiile himself, in his Cf«rs rf'£"(o"if-/c^:'', ' ' "" '^"■" 



mostraca (which he had sunk as a primary 



ten ye; 



section 



will be 

 leh they 



up the Ento- 

 ; class i 



favour uf sections cliaracturi^eil by the mouth organs) into fi\-e orders, 

 Liiphyropoila, Ostrapoda, I'hyllopoda, Xiphosura, and Siplionusloma, 

 and had characterized several sub-orders which Edwards subsequently 

 atli.pted iii the following sketch [SaUea de Biijfiin, Crust. I. p. 236, 

 modified from that published in the .'iininles dfs SiA. Nut., Murcb, 

 18:iUj. 



Subclass I.— Crustacea ^^■ith maxillai. 

 Legion 1. I'odopihalma. 

 Order 1 Dccapoda. 

 2. Stomapoda, 

 Legion 1. Eilrinpthalma. 

 Order 3. Amphipoda. 

 Order 4. Isopoda Order 5. Litmipoda. 



LcgioJi -2. Branchiopoda. Legion 3. Kntojnostraca. 



Order fl. Ostrapoda{Cythcrc). Order 8. Copepoda (Cyclops). 



7- Phyllopoda. 9. Cladocera(Uapbnia,a(C.) 



Legion 4. Trilobita. 

 Subclass \\. — Crustacea with asuckcr. 

 Legion 1. Ambulatory Parasites. 



Onler 10. Araneiformes (Pycnogonum). 

 Legion2.SwimmingParasi.es. 

 Order 11. Siphonosloma. 

 12. Leriie!e. 

 Subclass III.— Crustacea Xiphosura. 

 Order 13. Xipbosura. 

 Burmeister, in bis Gn^ndrifs fur K'liurgeiclnc/ile, Zr,;!ogisihn 

 II'i!idfitln.i, and Memoir on the Cirripedes, has divided the class into 

 three orders only:— 



