1900.] Wei<CH. — Abnormal Shells of Helix nemoralis. 167 



result in a thick shell, even when the other conditions also 

 seem favourable to weight or size, or both combined. 



Dr. Scharff kindly calls my attention to the fact that our 

 thickest British shell, Unio viargaritife7% lives in the mountain 

 streams of granite areas, where the amount of lime present 

 must be very small indeed. But for these, and some similar 

 cases, I would have ventured the opinion held by many others, 

 that thick shells were the result— in part at all events — of a 

 plentiful supply of lime in the animal's food. So far as these 

 heavy Bundoran shells are concerned, Dr. Scharff considers 

 that, possibly by the action of the salt spra}^, an abnormal or 

 pathological condition of the mantle is produced which may 

 explain the excessive deposition of lime in the shell. The 

 number of specimens found there which have an abnormal 

 continuation to the otherwise complete shell, like Figs. 10, and 

 II, seem to confirm the correctness of his conclusions. 



It would be interesting to know how long this species will 

 live under the specially favourable conditions present in many 

 places on the west coast of Ireland. I have some still alive 

 that were full grown when collected in September, 1898, on 

 the Belfast hills ; and the majority of 44 Helix aspersa collected 

 in October, 1S96, at Whitepark Bay, are now, after more than 

 three years, still alive. Some of these were quite adult and 

 fully a year old, I should say, when collected. They have 

 been well fed each summer, and protected from severe frost 

 in winter. 



EXPI^ANATION OF Pl.ATE 5- 



Figs. I — 8. Sinistral shells. 



,, loandii. Specimens with abnormal continuation to 

 the shell. 



,. 12 — 19, Scalariform specimens. 

 Fig. 8. Repaired and distorted sinistral shell. 



„ 9, Heav)', thick specimen, var. hyalozonta (50 grains). 



Belfast. 



