INTRODUCTION. 9 
and also Helix lapicida and H. nemoralis at the height of thirty or 
forty feet up beech trunks at Ewell. 
GEOLOGICAL FORMATION IN RELATION TO MOLLUSCAN LIFE. 
It may be remembered that peaty soils yield little or nothing. The 
red sandstone districts of the Midlands are very poor, though not so 
those in Devon; and the desolate and repulsive millstone-grit districts 
are particularly barren. 
The sandy and calcareous soil of the oolite formation on the other 
hand is not at all barren, except in places where it contains a large 
percentage of iron and little calcareous matter, as in the Northampton 
Sand. Sand hills by the sea are very favourite habitats for 
Helix nemoralis, H. aspersa, H. virgata, etc. 
Pine woods do not harbour molluscs—the resin perhaps being dis- 
tasteful to them. The bracken, too, is shunned by all species except 
Vertigo edentula. 
Calcareous districts are always fruitful, especially pure chalk, while 
granite and shale are not. 
I have observed that ponds surrounded by oak trees do not usually 
contain shells—perhaps the tannic acid does not agree with them. 
It is certain that there is some relation between plants and the soil 
and molluscs ; but of this relation very little is known, and there is 
therefore a wide field for observation and experiment. 
Brest TIME FOR COLLECTING. 
The times of the year when the most perfect specimens are 
obtained are— first, the early spring when the animals have just 
emerged from their winter-quarters and before they commence to forint 
a new lip; secondly, the autumn, just before they hibernate and after 
the formation of the lip. J think the spring is the best time for the 
aquatic and the autumn for the terrestrial species. All through the 
summer, of course, shells are to be found, and those with the im- 
mature lip, which is thin, should be handled and cleaned very carefully, 
