294 CRUSTACEA. 



night Some inhabit cemeteries. Once in the year they collect in immense 

 bands, and pursue a direct course to the sea, heedless of all obstacles ; after 

 depositing their ova, they return much enfeebled. It is said that they seal up 

 the mouth of their burrow during the time they are casting their shell. 



FAMILY II. 

 MACROURA*. 



IN the Decapoda M acroura, the end of the tail is provided with appendages 

 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 extre- 

 mity. 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 branchiae are formed of vesicular, 

 bearded and hairy pyramids, arranged in several of them, either in two rows, 

 or hi separate fasciculi. The antennte 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. 



With De 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 situations of their ova, 

 evidently approach the preceding Crustacea, and approximate still more 

 closely to those commonly known by the names of Crawfish, 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 swimming, and none of them terminate in 

 a forceps. The ova are situated between them, and not under the tail. 



This genus is now divided into four sections, each consisting of numerous 

 subgenera. In one of these (Pagurus) we find the Hermit (Cancer Bern- 

 hardus, Lin.) which inhabits univalve shells, stopping the aperture with its 



Ix>ng-tailed. 



