54 CRUSTACEA. 



FAMILY II. 



MACROURA. Exochnata, Fab. 



In the Decapoda Macroura, the end of the tail is provided 

 with appendages(l) which most frequently form a fin on each 

 side; the tail itself is at least as long as the body, extended; 

 exposed and simply 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 fila- 

 ments. This tail is always composed of seven distinct seg- 

 ments. 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 an- 

 tenn8e are generally elongated and salient. The ocular pedi- 

 cles 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 pre- 

 cited memoir of Messrs Audouin and Edwards. These gen- 

 tlemen have observed a character in the Lobster, Astacus 



(1) These appendages consist of three pieces, one of which serves as a base or 

 pedicle to the others, and is articulated with the penultimate segment; the latter, 

 in conjunction with them, usually forms a fan-like fin; but in the last subgenera of 

 this family these appendages are replaced by setaceous filaments. The false feet 

 under the tail are similar in their structure to these natatory appendages. In the 

 first subgenera they frequently do not exceed three or four pairs, and are smaller, 

 or even null in the males, the two anterior ones always excepted; the Paguri, as 

 it appears to me, only have them on one side: the terminal pieces are often une- 

 qual. In the succeeding ones, however, these feet are longer, and always form 

 five pairs; the ova attached to them, and they are used by the animal in swimming. 

 We observe that in the Macroura, where they are fewer in number, or less de- 

 veloped, as in those which we term the Anomala, the peduncle of the intermediate 

 antenna: is longer in proportion than in the others, and that the two or four last 

 four feet are smaller. These Crustacea, in some respects, seem also allied to the 

 Brachvura. 



