520 ^ilisses M. D. ILivilaii 1 and F. Pitt on the 



Certainly thrushes seem to destroy plenty of HelLv aspersa, 

 whose shell appears to be more iucoaspicuously coloured 

 than that of H. nenioralis. 



JNIr. Tinieman's tal)les do not give an exact idea of the 

 "• couspicaousness " of a given shell. For instance, a " two- 

 handed ' specimen might answer to the formula (123)(45) 

 and appear nearly black ; or it might be described as 00230 

 and look almost yellow. This would make all the difference 

 to its conspicuousness. But the figures given are certainly 

 curious, and two explanations suggest themselves : — 



(a) The possibility admitted by Mr. Trueman himself in 

 his last paragraph, when he says : " The figures 

 appear to show that banded shells are less liable 

 to be seen — or, at least, to be eaten." The italics 

 are mine. 



{b) That the darker varieties predominate in bushy 

 places and the lighter in the open, where the 

 thrushes generally feed. Hence the birds would 

 find a larger proportion of unhanded shells. 



With these ideas in view I made two series of observations 

 in the summer of 1917; I had hoped to continue them in 

 1918, but circumstances prevented this, and unfortunately 

 neither of them are as complete as they should be. 



The first experiments were made on Maidenhead Thicket, 

 in an open grassy place surrounded by bushes, between 

 June 25th and July 2nd. The snails were tethered to pegs 

 by black threads, varying from 6 to 12 feet in length, passed 

 through a hole drilled in the lip of the shell, and the numbers 

 were checked ever)' evenmg. Snails disappeared on the 

 second and succeeding days, but I did not oljtain positive 

 proof that they were taken by thrushes until June 30th. I 

 found a four-banded shell, still fastened to its thread but 

 unmistakably smashed by a thrush, and some yards away 

 was a second four-banded shell, also broken, beside a stone. 

 On the following day, in addition to two three-banded shells 

 which had been carried off altogether, I found three four- 

 banded shells which, with the threads still attached, were 

 lying each beside a stone with the shell smashed, but with 

 the animal uneaten. 



For convenience in working, the snails, whose tethering 

 threads became much entangled, were put out in five groups 

 — A, B, C, D, E. Each group consisted of from four to six 

 snails tied to one peg and selected quite haphazard. The 

 groups were all within an area of 25 yards, but A and B 

 were much overhung by bushes, C was a little more exposed, 

 and D and E were quite in the open. Four snails were 



