156 A HISTORY OF RECENT CRUSTACEA 
peduncle is compressed, the terminal joint long. The 
branchial plumes are laminar. 
The species are partially terrestrial. The family in- 
cludes two well-known genera. 
Birqus, 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 
branchize 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. Liesk 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 rownd its body, by the aid of its posterior 
