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 vesicular, 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, Avould be decisive ; it is, that besides 

 the two venous sinuses of which we have spoken in our general 

 observations upon the order, there is a third, situated 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 Crau--Jish, 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. They 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 will 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. 



