210 THE ZOOLOGIST. 
Among the litter of empty shells the presence of a variable 
number of unopened shells is of daily occurrence. 
Some are quite uninjured, the margins of the valves are in 
perfect apposition, and are tightly closed. More commonly the 
valves of each Mussel are rotated partially on one another, so 
that the margins overlap, and a portion of the mantle is nipped 
between the edge of one valve and the inside of the other. When 
the valves are not shut firmly this rotation is produced easily by 
applying pressure to the valves in opposite directions; the 
Mussel makes no attempt to readjust the relative position of the 
valves, and slowly adducts them in their altered relation. As 
might be inferred from what has been stated, the right valve is 
as a rule lower posteriorly than the left, and the dorsal border is 
uppermost as the shell lies on the ground. 
Shells which measure not more than an inch nor less than 
half an inch in length are searched for, and opened in the same 
way as the larger specimens, but the introduction of the bill 
and the subsequent manceuvres require less force, and are per- 
formed more rapidly. Frequently, however, the Oystercatcher 
approaches with the bill opened widely, and pushes the upper 
mandible between the valves; simultaneous rotation of the head 
to one side on a vertical axis and approach of the lower to the 
upper mandible follow, so that the upper mandible rotates into 
a transverse position within the fissure, and the posterior portion 
of one valve is crushed and twisted outwards in the firm grip of. 
the bill. 
Shells of half an inch by quarter of an inch and those of 
smaller size are torn from the rocks, one at a time, and are 
“swallowed entire. Macgillivray,* speaking of the contents of 
the stomachs, states that the bivalve shells are generally, 
‘“‘“when of small size, either entire or merely crushed”; and 
Professor Patten t has found “in several gizzards small bivalves 
with unbroken shells which measured 12 by 5 mm.” 
The greater part of the mollusc makes a few mouthfuls. 
Large pieces are torn away and transferred to within reach of 
the tongue by jerks of the head. At each projection of the head 
the bill, as it were, slides over the piece, and the return of the 
* ¢ History of British Birds,’ vol. iv. p. 156. 
+ ‘Aquatic Birds of Great Britain and Ireland,’ p. 249. 
