420 
CRUSTACEA. 
claws are nearly equal, consisting also of a single species (A^ius stirhynchus, Leacli) found upon the coasts of 
England and France. 
Amongst those species which have the six fore-legs fonning as many didactyle claws— (a character which removes 
them from all the preceding Decapods, and in which they are related to the species at the head of the following 
section— from which, however, they differ in the fore-claws being by far the largest, the peduncle of the lateral 
antennae furnished with a scale or spines, the outer plate of the swimmeret at the extremity of the tail appeal ing 
in all the recent species, as though it is divided into two parts by a transverse suture,)— are the following genera. 
Eryon, Desm., comprises a single singular fossil species found in the calcareous stone used for lithography at 
Pappenheim and Aichtedt, in Anspach. The carapax is [very broad], and with very deep lateral incisions. The 
plates of the swimmeret are pointed at the tip. 
The genus Astacus, Gronovius, Fabr., have the lateral plates of the swimmeret broad and rounded at the ex- 
tremity ; the two exterior ones with a transverse suture. The two filaments of the intermediate antennae are 
longer than their peduncles, with the sides of the carapax entire. 
In the marine species of this genus, the middle plate of the tail does not exhibit a transverse suture. Of some 
of these, Leach has formed his genus Nephrops, characterized by the large scale of the lateral antennae, and the 
long prismatic claws of the fore-legs. Type, Cancer norvegicus, Linn., a species found on our coast. The 
others having the lateral antenna only furnished with two short teeth or spines, and the fore-claws large and oval, 
form the restricted genus Astacus, Leach, the type of which is the common Lobster {Cancer gammarus, Linn. ; 
Astacus marinus, Fabr.), of which the rostrum in front of the carapax is armed with three teeth on each side, and 
a double tooth at the base ; and the claws are very large, and unequal in size. The flesh is highly relished. It is 
found in the European Ocean, the Mediterranean, and on the coasts of North America. The internal structure 
has been studied with great diligence by MM. V. Audouin and M. Edwards. 
In the fresh-water species of this genus, the terminal segment of the tail, forming the middle plate of the swim- 
meret is transversely divided by a suture*; and the claws are rough, and finely toothed on the inside of the 
fino-ers The rostrum has a tooth on each side, and two at the base. It is ordinarily of a greenish-brown colour, 
[but, like the lobster, changes to bright red by boiling]. From its common occurrence it has been greatly studied, 
^ ’ not only as regards its anatomy, but also its habits, 
and the peculiar power it possesses of renewing its 
antennae and legs when thrown off" or mutilated. 
The stomach contains, at the time of moulting, two 
stony secretions, formerly used in medicine as ab- 
sorbents, but which are now replaced by carbonate 
of magnesia. It hides itself under stones and in 
burrows [in the banks of rivulets and streams], 
whence it only comes forth in order to search for 
its food, which consists of small mollusca, small 
fishes, and the larv« of aquatic insects. It also 
feeds upon decaying flesh, and the carcases of ani- 
mals floating in the water ; and which is also used 
as a bait, being placed in the middle of a bundle of faggots, or in a net. Its moulting takes place at the end of 
the spring. Two months after coupling, the female lays her eggs, which are at first collected in a mass, and 
attached, by means of a viscid liquor, to the subabdominal false legs. They are of a bright red colour, and in- , 
crease in size before they are hatched. The Crayfish are at their birth very soft, and completely resemble their 
parent. They take refuge beneath her tail, where they remain several days until the different parts of their bodies 
have acquired a sufficient strength. They live to the age of twenty years, increasing in size in proportion to their 
age. Those are preferred which are found in running water. A singular Annelidous parasite {Branchiobdella, 
Odier, in Mem. Soc. d’Hist. Nat., Paris, p. 69 ), first observed by Rosel, infests the branchiae of the Crayfish. ^ 
Another species inhabits the fresh water of North America; and a third, according to Le Conte, does much in- , 
jury to the rice plantations of the same country.t 
The fourth section, Carides (Latr.), have the intermediate antennae inserted higher than the lateral, 
and the peduncle of the latter is covered by a large scale. The body is arched, as though hunch- 
backed, and of a more slender consistence than in the preceding Crustacea. The front of the carapax i 
* [Milne Edwards, from having adopted an evidently improper mode 
of nomenclature, has taken away from the two best known .Decapod 
Crustacea, the old generic names which they are clearly entitled to 
retain. Thus he calls the common Crab, which is the true type of 
the genus Cancer, Platycarcinus-, against which impropriety Mr. Bell 
has well remarked, that by any other term than Cancer to this genus, 
we are obliged to restrict the word Cancer to a small and compara- 
tively unimportant group, not a single species of which was probably 
distiimtly known to any naturalist of early times. In iike manner, he 
has taken away the name Astacus from the Lobster, and given it to 
the Craytish, and proposed tlie new name Homarus for the former : 
thus doing injustice to Dr. Leach, who, in the manuscripts 
quoted in the Entomologist’s Compendium (witli whicli Milne 
Edwards is evidently unacquainted), had called the Lobster 
gammarus, and the Crayfish Potamobius ftuviatilis. It is proper. 
however, to observe, that the latter had been named Cancer astacus 
by Linnoeus.] 
t [The developement of the embryo Crayfish, in the egg, has been 
investigated by Dr. Rathke, in a most elaborate and satisfactory man- 
ner, in his Untersuchungen uber die Bildung und Entwichelung der 
Flusskrebsen, fol. Leipz. 1829. Some idea of the extent of the re- 
searches of this author upon the subject may be entertained from the 
fact that five large folio plates are completely filled with details of the 
structure, internal and external, of the ova, in various states of de- 
velopement, and of the newly-hatched animal, from whence it is im- 
possible to arrive at any other conclusion than that the Crayfish does 
not undergo any change of form which can in the least degree merit 
the name of metamorphosis. A full abstract of this valuable memoir 
is inserted in No. 18 of the Zoological Journal, and in the Annales 
des Sciences Naturelles for August, 1831.] 
