20 
J. HOPKINSON-REMARKS 
only thing which will drive some species into the light of day; 
some will even climb trees on such occasions. 
The best time, therefore, to find the land Mollusca in the open 
country is in the early morning, before the dew of night has 
evaporated, or, if later in the day, immediately after rain. In 
woods sunshine is desirable in order the more readily to perceive 
the minuter forms. But at whatever time and whatever the 
weather may be, “ under-sides ” should not he neglected; every 
thing met with lying upon the ground under which they may be 
secreted should be turned over and examined; even a heap of 
stones by the road-side, especially if it has been long undisturbed 
and contains pieces of limestone or unwaterworn chalk-flints, should 
not be neglected, and a piece of old matting which has long lain on 
the ground may prove a fruitful field for research. One thing I 
think they do not like, and that is leather ; I never hut once found 
a slug or a snail under an old hoot. 
Some species delight in damp moss ; these are generally the 
minuter forms, and therefore the moss requires very careful scrutiny. 
Moss growing on fallen branches of trees is perhaps a better hunting- 
ground than moss growing on stones, but damp moss in whatever 
position, if sheltered from the rays of the sun, may yield a rich 
harvest. Other species again only occur on vegetation growing on 
marshy ground. 
Prom the foregoing remarks it may have already been inferred 
that the terrestrial Mollusca were in all probability originally the 
denizens only of forests or woods, especially such as are watered by 
numerous streams or abound in marshy places; and this view seems 
to be borne out by the habits of the indigenous land mollusks of 
North America. These are almost exclusively found in dense 
forests, by the clearing of which they are exterminated, the pro¬ 
gress of agriculture and consequent alteration in the natural aspects 
of the country being so rapid that they have not time to accommo¬ 
date their habits to these new conditions. In Europe the clearing 
of forests has been a much slower process, and appears to have 
given time for some at least of our Mollusca to accommodate them¬ 
selves to more open situations. It would seem, therefore, that it is 
in consequence of this adaptability of our species to altered condi¬ 
tions, that several of these which have been introduced accidentally 
by man to the North American continent have readily become 
acclimatised, and are taking the place of the indigenous species, 
supplanting them as surely as the native races of man are being 
exterminated by those of European origin.* 4 
Hertfordshire is still a well-wooded county, but at one time the 
greater part of it was probably a dense forest; being also a well- 
watered county, with not too-rapid rivers, we may presume that 
formerly both the land and the fresh-water Mollusca found here 
a most congenial habitat, and with their power of rapid increase 
would swarm in vast numbers amongst the luxuriant vegetation, 
* See Binney’s ‘ Terrestrial Air-breathing Molluscs of the United States . . . 
yol. v, pp. 2, 3. 
