DECAPODA. 
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The lateral edges of the carapax are bent downwards in order to cover and defend the 
branchiae, an aperture being left in front of the shell for the passage of the water.* The 
branchiae 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, applied to the mouth and 
divided into two branches, the exterior resembling a small antenna, furnished at the tip with i 
a short multiarticulate pieee [and the interior composed of several joints, the two basal being 
greatly dilated in the crabs], the base being also furnished with a long pilose tendinous branch. 
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, which is moveable, and is named the pollex, whilst the 
other is fixed, and is named the index. In Squilla the last joint is very short, and then the 
penultimate joint folds baek upon the preeeding. The antepenultimate joint is the carpus. 
The respeetive proportions and situation of their limbs is such that these creatures are able to 
walk sideways or backwards [crab-like]. 
The majority of the viscera are inclosed in the thorax, which thus represents the thorax 
and greater part of the abdomen of the insects ; the terminal articulated parts of the body 
immediately following those segments to which the five pairs of true legs are attached, con- 
stitute the part which I name the post-abdomen. The stomach is armed within with five 
bony and dentated pieces which serve to triturate the food. At the time of moulting, two 
caleareous bodies, round on one side and flat on the other, are found in the stomach, 
which are ordinarily called crabs-eyes, and which, as they disappear after moulting, have 
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 find the largest species of annulosa, as well as the most useful as articles of 
food ; their flesh is, however, hard of digestion. The body of some species of Palinurus is 
more than a foot in length. Their claws, as is well known, are extremely pow'erful. They 
ordinarily reside in the water, but are not immediately killed by being removed into the air : 
indeed, some species pass a considerable part of their existence out of the water, which they 
only seek in order to deposit their eggs in it. They are, nevertheless, compelled to reside in 
damp situations and burrows. They are naturally voracious and carnivorous : some species, 
indeed, are said to frequent the cemeteries in order to feed upon dead bodies. Their limbs 
are renewed [when injured] with great quickness, but it is necessary that the fracture should 
have been made at the junction of the joints : they, however, have theinstinet to effect this if 
the wound has been of a different nature. When desirous to change their skins, they seek 
for some retired spot, where they may be at rest and secure from their enemies. The moult- 
ing then takes plaee, the body being at first soft and of a delicate flavour, [as in the case of the 
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 
different proportions. By the action of the heat the epidermis assumes a bright red colour, 
the colouring principle being decomposed by the action of boiling water. 
The greater number of fossil Crustacea hitherto discovered belong to the order of Decapoda. 
Amongst the European fossil species, the most ancient approach nearest to the existing species 
found in tropical seas, while the more modern ones have a greater resemblance 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 faet of considerable geological 
interest. [The order contains two families, or rather sub-orders, named, from the comparative 
size of the tail, Brachyura (short tailed) and Macroura or Macrura (long tailed.)f] 
* MM. Audouin and Milne Edwards have communicated to the I the blood during a considerable period]. It is on this account that 
Academie des Sciences some interesting observations upon a peculiar these crabs have the sides of the thorax more gibbose than ordinary, 
organ which exists in the Land Crabs, forming a kind of reservoir, ( t [M. Edwards proposed the establishment of a third sub-order under 
placed immediately above the branchiae, and capable of containing a | the name of Anoraoura, forming a passage between the two other 
certain quantity of water [serving of course for the oxygenation of I groups, and composed of species belonging strictly to neither, which 
