156 A HISTOBY OF EECENT CRUSTACEA 



peduncle is compressed, the terminal joint long. Tlie 

 brancliial plumes are laminar. 



The species are partially terrestrial. The family in- 

 cludes two well-known genera. 



Birgus, Leach, 1815, is a genus of eminent distinction. 

 The broadly ovate carapace covers large branchial cham- 

 bers, of which, however, the fourteen pairs of small 

 branchiae only occupy a small fraction, but on the other 

 hand, in evident adaptation to an aerial life, the lining 

 membrane of the chambers is covered with vascular pul- 

 monary outgrowths. The pleon is not twisted. It is very 

 broad. Dorsally its first segment is represented by a 

 corneous band, as the four following are by four corneo- 

 calcareous overlapping plates, flanked by small corneous 

 pieces which seem to represent the side-plates. The 

 second, third, and fourth segments have a large biramous 

 appendage on the left side, but only in the female. All 

 the underside of the pleon is membranous, until a quadri- 

 lateral plate is reached which represents the sixth segment 

 and which gives attachment to a rudimentary appendage 

 on each side and to the terminally rounded telson. 



The account given by Darwin of that which is probably 

 the type and perhaps the only species of this genus is too 

 interesting to be omitted. When treating of the Coral 

 Islands of the Pacific, he says : — ' I have before alluded to 

 a crab which lives on the cocoa-nuts : it is very common 

 on all parts of the dry land, and grows to a monstrous 

 size ; it is closely allied or identical with the Birgos latro. 

 The front pair of legs terminate in very strong and heavy 

 pincers, and the last pair are fitted with others weaker 

 and much narrower. It would at first be thought quite 

 impossible for a crab to open a strong cocoa-nut covered 

 with the husk ; but Mr. Ijiesk assures me that he has re- 

 peatedly seen this effected. The crab begins by tearing 

 the husk, fibre by fibre, and always from that end under 

 which the three eye-holes are situated ; when this is com- 

 pleted, the crab commences hammering with its heavy 

 claws on one of the eye-holes till an opening is made. 

 Then turning round its body, by the aid of its posterior 



