GEOGRAPHICAL DISTRIBUTION. I39 
character of the plants ; and it is likely that both of 
them have their influence. The mechanical properties 
of the soil also have an influence, as in the instance of 
sand, to which we have alluded. So too, a soil composed 
of stiff clay which on a few hours exposure to the sun 
becomes baked and rigid, and cannot be penetrated by 
them, is ecpually unfavorable. There are other localities 
'where individuals multiply infinitely. Mr. Anthony, of 
Cincinnati, Ohio, informs us, that in his walks around 
that city, himself and a friend collected during a single 
week, above five thousand specimens of Helices, the time 
devoted to the walks being taken from the intervals 
between business hours, and good and mature specimens 
only being selected. Professor Adams states that he 
collected, in one hour, more than one thousand specimens 
of Helix minuscula ; and Dr. Gould found Bulimus 
lubrieus so abundant upon Oak Island, that many hun- 
dreds could be taken from the ground with a single 
handful of decaying leaves. 
Although some few species seem to occupy somewhat 
li m ited localities, not having as yet been found over any 
very broad region, yet the range of most species is very 
extensive ; and, what is worthy of remark, the widest 
distribution is to be noticed in the smallest species. The 
smaller species are also tenfold, and probably a hundred- 
fold more numerous than the larger. This circum- 
stance is somewhat difficult of explanation. Both their 
number and their broad range may perhaps be owing 
to their very diminutiveness, on account of which they 
