Order 1. DECAPODA. , 411 



The lateral edges of the carapax are bent downwards in order to cover and defend the 

 branchiae, an apertin-e 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, ap])lied to the mouth and 

 divided into two branches, the exterior resembling a small antenna, furnished at the tip with 

 a short raultiarticulate piece [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 back upon the preceding. The antepenultimate joint is the carpus. 

 The respective 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 rejiresents 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 

 calcareous 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 powerful. 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 the instinct 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 place, 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 boihng 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 fact 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. )t] 



* MM. Audouin and Milne Edwards have communicated to the 

 Academie des Sciences some interesting observations upon a peculiar 

 orjfan which exists in the Land Crabs, forming a kind of reservoir, 



the blood during: a considerable period]. It is on this account that 

 these crabs have the sides of the thorax more gibbose than ordinary, 

 t [M. Kdwards proposed the establishment of a third sub-order uuder 



placed immetliateiy above the branchije, and capable of containing a j the name of Anotnoura, forming a passage between the two other 

 certain quantity of water [serving of course for the oxygenation of ' groups, and composed of species belonging strictly to neither, which 



