240 The Bird 
then pried open and eaten. The bill of this bird shows 
the wear and tear of forcing apart the shells, and it is 
sometimes slightly bent to one side. The short-billed 
gulls are denied the power of opening these oysters and 
mussels, but they sometimes get an unlawful feast by fol- 
lowing up and robbing the Oyster-catchers of the shells 
which the latter have opened. 
The bill of the Shell Ibis of India may be likened to 
an ordinary lemon-squeezer, having a cavity in which 
Fic. 184.—Bill of Oyster-catcher; used for prying open the shells of mollusks. 
the half-lemon rests before it is compressed. When 
the mandibles of this bird are closely opposed the central 
portion of the beak gapes slightly. In this cavity the 
bird firmly holds the shells of the land-snails upon which 
it feeds, until it can bring the pressure of both mandibles 
to bear and so crush the shell of the mollusk. 
The asymmetry of the bill—as seen in the Oyster- 
catcher—is not accidental, but constant, in the Crook- 
billed Plover of New Zealand. In this bird the bill is 
