410 



CRUSTACEA. 



The singular fossils called Trilobites, of wliieli M. Brongniart lias fumislicd an 

 excellent monograiih, being considered by him and many other naturalists as cru-;- 

 taceous animals allied to the Entomostraca, we have introduced them concisely at the 



end of that section. 



FIRST GENERAL DIVISION. 



CRUSTACEA JIALACOSTRACA,- 



^^ hich are divisible into those which have the eyes placed on a moveable foot-st.alk, 

 and those which have them sessile and fixed. 



I'bose Malacostraca with the eyes placed on a moveable foot-stalk, articulated 

 [at the base, Podoptiialma, Leach], composing the orders Decapoda and Stomapoda, 

 have many characters in connnon. A large shield, sometimes divided into two parts, 

 and termed the shell or carapax, covers a large portion of the front of the body. I'hey 

 have four antenna\ the exterior jiair being longest and simjde, wdiilst the intermediate 

 pair is shorter, and divided at the tip into two branches in the crabs, and into three in 

 many of the Macrura ; two mandibles, each with a three-jointed palpus near the base, 

 a bilobed tongue, two pairs of maxillfe, three pairs of foot-jaws, the two outer pairs 

 being in some [Squilla] transformed into claws, and ten or fourteen (in those species 

 which have the four outer foot-jaws leg-shaped) legs. 



In the majority the brancbiic, of which there arc seven pairs, are hidden beneath the 

 lateral margins of the carapax, the two anterior jiairs being fi.\cd at the liase of the two 

 exterior pairs of foot-jaws, and the others at the base of the true legs. In the other 

 species [Squilla, &c.] they form brushes attached to the five pairs of sub-abdominal 

 swimming legs. I'lie under side of this post-abdomen is likewise furnished in the 

 others with tour or five pairs of bifid appendages. 



THE EIKST ORDER OF CRUSTACEA. 



DI'.rAl'ODA (Tl'.\-F( lOTEDI. 



Tlie h'ad is compaplly soldered to the thorax, and covered, as well as that part of the body, 

 liv a \:ii''iy and Cfintnuinus sliell nr carapax, generally exlnbitmg ou its surface varK>us 

 impressed Imcs, di\iilin!j; it uito re^jious corresponding with the internal organs, and which 

 have been higeniously named hy iM. Dcsmarest. The circulatory system differs in some 

 respects from that of the other Crustacea; the blood before reaching the brancbiie to Ije 

 oxyg-enatcd passing through two great reservoirs, one on each side, above the legs, analogous 

 to tlir lateral hearts of the Ccphalopods, acconliiig to ililue Edwards, Audouin, and Cuvicr. 



1. A.i)iiliisIrnco, divUlcd into fivt, Biil'-oriliTS. 



1. f.r^.sita, includirjn the PejiuUina. Leriiteo'l^i, EryaMlina, 



.■»liu-ii.a, nnilArgull,,™. 



2. Lopliynipodii, iiicluiiiiig tlic Ostracoiln, Claducfra, and 



CyclopiUa. 



3. Pliyllipocitt, includiiiK thu Gymnnta (Br.inuliiL'Us), antl Ab- 



pidoplmra {Ajjus). 



4. Cirripeclia, Includhjif the Lcpariea and D.-.lanorln, 



5. PrEcilopoda, inclurlijip „\\\y Xipliusura. 



2. Thoracostriifii {Pixt'^pthnh-'i, Luin:li), liivideii iiiiii (wo suborders, 



Dccapuda and Stomapoda. 



3. AnhTOtflnca {Edriupt't'il,,,'!, Lr:i^\i), divided iiUo nirjc- riiiiii-.r 



divisions, Gamm.ariun, Typliioa, LccmoilipnUn, Epie/irida, Cymo- 

 tliiKtda;, Sphffiraaiiitoda, Aacllina, Idutodn, ainl Uni^cuil.i. 



De Hnan, in his mfignilicent work upon lh>: Crustiicea of Japan, 

 adoptiuK the qiiinari/iii circular system of Rl'Leay, divides the class 

 into five ordt^rs.—Decnpuda.Stomapoda, Tetrad tcnpnd.i(£drfo;>Mrt/m'f, 

 Leach), Lophyropoda, and Pliyllopoita. M. Duvcrney has, within the 

 last few months, submitted a Memoir to tf.c Academic des Sciences nt 

 Paris, propnsiijg a new chssificatioii u( i Crustdeea aecontiiii,' to the 

 orKans of respiration, dividing the class inin three prineipHi j,'!-!^!!.*, 

 Nudihranchia];, CryptohraiieliitE, and Lamcllibranchio: ; but tliendi.p- 

 tioii of tills, like any other single cl> -acter, lias had the cffuct of 



;il,e 



:al rclai 



