190 
CRUSTACEA. 
curved towards its posterior extremity. Its under surface usually 
presents in both sexes five pairs of false feet, each terminated by two 
laminae, or as many filaments. This tail is always composed 
of seven distinct segments. The genital orifices of the females 
are on the first joint of the third pair of feet. The branchiae are 
formed of vesicidar, bearded and hairy pyramids, arranged in several 
of them either in two rows, or in separate fasciculi. The antennae 
are generally elongated and salient. The ocular pedicles are usually 
short. The external foot-jaws are mostly narrow and elongated, 
resembling palpi, and do not wholly cover the other parts of the 
mouth. The shell is narrower and more elongated than that of the 
Brachyura, and usually terminates by a point in the middle of the 
front. 
For more minute details we refer the reader to the precited memoir 
of Messrs. Audouin and Edwards. These gentlemen have observed 
a character in the Lobster , — Astacus marinus, Fab. — which, if it 
applied to the other Macroura, would be decisive ; it is, that besides 
the two venous sinuses of which we have spoken in our general 
observations upon tbe order, there is a third, sitiiated in the sternal 
canal between the two preceding ones, and extending from one end of 
the thorax to the other. This curious arrangement, according to 
them, establishes a connexion between the venous system of the 
Macroura, and that of the Stomapoda. 
The Macroura never quit the water, and, with the exception of a 
small number, are all marine Crustacea. 
In imitation of Dee Geer and Gronovius, we will arrange them 
in a single genus *, that of Astacus, which we divide in the following 
manner ; 
Some, by the proportions, figure, and uses of their feet, of which 
the first, or at least the second pair, are in the form of claws, and by 
the subcaudal situation of their ova, evidently approach the preceding 
Crustacea, and approximate still more closely to those commonly 
known by the names of Craw-fish, Lobster, and Shrimp. 
The feet of the others are very slender, and are furnished with an 
exterior and elongated appendage or branch, which seems to double 
their number. I'hey are exclusively adapted for natation, and none 
of them terminates in a forceps. The ova are situated between them, 
and not under the tail. 
We will subdivide the former into four sections; the Anomala, the 
Locusts, the Astacina, and the Carides. 
The latter Avill compose the fifth and last sections of this family, 
and of the Decapoda, or that of the Schizopoda. 
In the first, or the Anomala, the two or four last feet are always 
* The sections which we are about to describe might form so many generic divi- 
sions, having for their basis the genera of Fabricius. 
