DECAPODA. 4 i 1 



Tlie lateral eflges of the oarapax are Ijent tloivinvanls in onler to cover ami defend tlie 

 brancliia;, an aperture being left in front of the shell for the passage of the water.* The 

 Ijranehitc are situated at the base of the four exterior foot-jaws and of the legs, the four 

 anterior being smallest. The six foot-jaws are of a different form, apphed to the month and 

 divided into two branehes, the exterior resembling a small antenna, furnished at the tip i\itli 

 a short multiarticulate piece [aud the interior composed of several joints, the two basal being 

 greatlj' dilated in the crabs], the base bemgalso furnished with a long pilose tendinous Ijranch. 

 The anterior pair of legs, and sometimes the two or four following, form large claws, the 

 penultimate joint being dilated, with its lower extremity prolonged into a finger opposed to 

 the terminal joints or true tragus, wdiieh is moveable, and is named the pfiUex, whilst the 

 other is fixed, and is named the index. In Squdla the last joint is ver)' short, and then tlie 

 penultimate joint folds back upon the preceding. The antepenultimate joint is the carjjus. 

 The respective proportions and situation of their limbs is such that these creatures are able to 

 wallc sideways or backwards [crab-like]. 



The majority of the viscera are inclosed in the thorax, which thus rejiresents the thorax 

 and greater jiart of the abdomen of the insects ; tlie terminal articulated [larts of the liody 

 immediately following those segments to which the five pairs of true legs are attached, con- 

 stitute the part wdiich I name tlie post-abdomen. The .stomach is armed within witli five 

 bony and dentated pieces which serve to triturate the food. At the time of moulting, two 

 calcareous bodies, round on one side and flat on the otlier, are found in tlie stomach, 

 wdii(di are ordinarily called crabs-eyes, aud wdiich, as they disappear after moulting, liave 

 been considered to furnish the material for the renewal of the carapax. 



The growth of these animals is slow, and they live for a long time. It is amongst these 

 animals that we fiu<l the largest species of annulosa, as well as the most useful as articles of 

 food ; tlieir flesh is, however, hard of digestion. The body of some species of Palinurus is 

 more than a foot in length. Tlieir claws, as is well known, are extremely powerful. Tliey 

 ordinarily reside in the water, but are not immediately killed by being removed iuto the an- : 

 indeed, some species pass a considerable part of their existence out of the water, wliicli they 

 oulv seek in order to deposit their eggs in it. They are, nevertheless, compelled to reside in 

 damp situations aud liurrows. They are naturally voracious and carnivorous : some species, 

 indeed, are said to i'requent the cemeteries in order to feed upon dead bodies. Their limbs 

 are renewed [Hhen injured] mtli great quickness, liut it is necessary that the fracture should 

 have been maile at the junction of the joints : thej', however, have the instinct to eifect this if 

 the wound has lieeu of a different nature. When desirous to change their skius, they seek 

 for some retired spot, ivliere they may be at rest aud secure from their enemies. The moult- 

 in"- then takes place, the body being at first soft and of a delicate flavour, [as in the ease of tlie 

 black crab of the West Indies, which is kept in cages expressly for the table]. The chemical 

 analysis of the old shell proves that it is formed of carbonate of lime and phosphate of lime in 

 diil'erent proportions. By the action of the heat the epidermis assumes a bright rod colour, 

 the colouring principle being decomposed by the action of boiling water. 



The greater number of fossil Crustaeca hitherto discovered belong to the order of Decapoda. 

 Aiiionn;st the European fossil species, the must ancient approach nearest to the existing species 

 found in tropical seas, whih- the more modern ones liave a greater resemhlanee to the species 

 now existing in our own climates. The fossil Crustacea of tropical regions bear a greater re- 

 lation to the existing species found in the same situations — a fact of considerable geological 

 interest. [The order contains two famiUes, or rather sub-orders, named, from the comparative 

 size of the tail, Brachyura (short tailed) and Macroura or Macrura (long tailed. )t] 



iratoH to lliL' I the blood during a consider.-iblc period]. It is or this iiccouiit that 



' MM. Audouiii 



■ des SLictiees sooic iiitLTestiog obstrvatioii^ upon a peculiar these crabs have the sides of the tborav more gibbose thai 



nrer.ui which ■ 

 pi K.- d i„.,uedi: 



tlic Lniirl Crabs, forming: a luiid of reservoir, | t [H. Eclwnrcla proposed the estnlilishmeiU of a third sub- order umie 

 ■ly above the ))raiichi;c, imd capable uf cont.iiiiin^' a | the name of Ajiomourn, forminjr a pissajjc bctivecn the twn othc 

 of water [stTVii't o^ course for the oxyijeiintioii of ' groups, and composed of species beloiif,niiir strictly to iieillier, whic 



