142 INTRODUCTION. 
striking example among them occurs in Helix pulchella. 
Tliis diminutive species is spread throughout the con- 
tinent of Europe ; it is common in the north of Africa, 
and in some parts of the south of Asia ; ' it is found in 
Cuba, and others of the West Indian islands ; and is 
abundant in nearly every part of the United States and 
Canada. The various positions which it is thus found 
to occupy, and the dissimilar circumstances in which it 
exists, together with the difference of cliinate and other 
physical agents to which it is subjected, and the vast dis- 
tances both of land and ocean which intervene between 
these localities, render it doubtful whether its general 
dispersion is not due to other causes than those which 
have been named, and whether, indeed, it can be ex- 
plained on any acknowledged principles. Its condition 
in this country tends to increase these doubts. Its occur- 
rence might, of course, be expected, in any country 
which has been closely connected with Europe by com- 
merce, but this would be no reason for meeting it in the 
interior of North America, far removed from the settle- 
ments of white men, and in places still inhabited by the 
aboriginal races, and only occasionally visited by the 
wandering hunter. Yet, in 1820, on the arrival of 
Major Long's exploring expedition at Council Bluffs, on 
the Missouri River, five hundred miles above its cmbou- 
1 Specimens of Helix pulcheUa were brought lo this country by Mr. 
Lyell, which were obtained by Lieut. Lyell, in the neighborhood of Can- 
dahar. They differ in no respectfrom common European ;>nd American 
specimens. 
