56 THE ZOOLOGIST. 



shell, with its sides parallel and not at right angles to the 

 ground. But the Limpet is well able to retain its hold, owing 

 apparently to the slight separation of the foot from the rock. 

 No rushing sound is heard. Leverage proves impossible, and 

 when it is tried the steel instrument bends under the strain to 

 the point of snapping. Further, its withdrawal, after the failure 

 to overturn the Limpet, is a matter of very real difficulty. 

 Thus the use of the bill, with its sides vertical to the ground, is 

 an advantage and a safeguard. It necessitates the edge of the 

 shell being raised to a greater height than is the case when the 

 bill is used flatly ; it favours, by this greater separation, first, of 

 the edge of the shell, and, secondly, of the edge of the foot from 

 the rock, the entrance of air or water under the foot ; and it 

 renders the withdrawal of the bill from under the Limpet more 

 easy in the event of failure. 



Though in the above description I virtually make out that 

 the admittance of air or water is essential to the overturning of 

 the shells, my strict position is that in many cases a rushing 

 sound is heard just before a shell which is out of the tide topples 

 over, and the sound is more like that of air entering a vacuum 

 than of air escaping from a cavity under pressure. 



Tectura (Acalea) testudinalis. 

 I found one shell of this genus and species amongst a quantity 

 of Limpets which had been overturned by the Oystercatcher. It 

 measured five-eighths of an inch in length by half an inch in 

 breadth (§ in. x £ in.), and was fractured at the larger end. 

 Some friable material still remained along the line where the 

 body of the animal had been attached. The record is interest- 

 ing, if only on account of the evenness of the edge of the shell, 

 which does not favour an attack at any particular part of the 

 circumference. 



