206 THE ZO00LOGIST. 
this position the bill is pushed in firmly until the point seems to 
reach the anterior end of the Mussel, when snapping motions of 
the mandibles occur, and are followed by gradual separation of 
the valves. It is plain that this method cannot be applied to 
Mussels buried in sand. 
When the empty shells are examined it is found that, with 
the exception of those opened by the last method, one valve in 
each is fractured—that the fracture extends in most cases from 
a point on the dorsal border of the valve, one-eighth of an inch 
from the posterior end of the ligament, along a curved course 
following one of the lines of growth to the anterior end of the 
shell, and passes above the insertion of the anterior adductor 
muscle. 
The upper and anterior fragment of the valve is raised by the 
passive contraction of the ligament, and its posterior free end is 
twisted outwards. Less frequently the fracture turns backwards 
instead of forwards, separating an upper and posterior portion 
from the rest of the valve. Occasionally the fracture extends 
transversely across the valve, isolating the posterior portion, 
and more rarely from the ventral border transversely across 
the valve to a point about a quarter of an inch below the pos- 
terior end of the ligament, and then horizontally to the 
anterior end. 
In this case the lower and anterior portion of the valve is 
separated, the posterior portion united to the upper and anterior 
portion remains with the other valve, and from posterior end of 
the ligament is twisted markedly outwards. 
It is noteworthy that the edges of the valves seldom show 
where the bill has been introduced. In the only example I have 
seen the margins of the valves a little behind the posterior end 
of the ligament were ground away, so that when the valves were 
brought together an elliptical hole was formed, which admitted 
the deepest part of a bill lengthwise... 
It can be shown experimentally that the fracture starts at 
the place where pressure is applied, and when the lever is rotated 
between the valves it begins at that edge of the lever towards 
which pressure is directed. On a few occasions these processes 
were verified by observing the Oystercatchers at work, and after- 
wards by examining the particular shells they had opened. 
