SUB-ORDER BRACHYURA. 95 



gradually increasing in size, furnished with palpi, the largest 

 of which is the external pair first mentioned above. Beneath 



small edible Crab). 



the antennae is also placed a pair of apertures, which have 

 been regarded as organs of hearing. The members which 

 immediately succeed the external foot-jaws constitute the 

 legs, and are also five pair in number (e, f, g, h, i) ; they 

 vary considerably in size ; those of the first pair are always 

 prehensile, and terminated by a didactyle and well-formed 

 claw ; in general, the four posterior pairs of legs are simply 

 ambulatory or natatory, they are never didactyle. The ab- 

 domen (k) is but slightly developed, its length never exceed- 

 ing three-fourths of that of the entire body, and its thickness 

 not equal to more than one-sixth or one-tenth of the body, 

 being in fact lamellose, and always closely applied to the 

 sternal excavation. It is essentially composed of seven seg- 

 ments, but it often occurs that some of these are so inti- 

 mately soldered together, that this part of the body appears 



