™ 
362 HELIX HORTENSIS. 
in its organization it is also quite different from and immensely superior to 
the Protogona,' the general helicidian type characteristic of Eastern North 
America, which, according to Dr. Pilsbry, has a very simple and primitive 
structure; yet the distributional area of //. hortensis, extending as it does 
along more than a thousand miles of coast and its occupancy of numerous 
rocky islets uninhabitable by man, combined with the discovery of its 
presence in the Pleistocene clays of Maine, lend support to the view that 
it has reached that country through natural diffusion, by means of the 
land-bridge, believed by many to have connected North-western’ Europe 
with North America during 'l'ertiary times, and by means of which a few 
other terrestrial species of boreal distribution have probably also reached 
Eastern North America. 
On the European continent it is said to be more or less completely 
diffused in France, Germany, Netherlands, Switzerland, Austro-Hungary, 
Denmark, Russia, Italy, Spain, Scandinavia, and Balkan Penimsula, but 
unfortunately implicit reliance cannot be placed on the correct specific 
allocation of all the records of this or the preceding species. 
It is recorded by M. Locard as inhabiting the Amoor Valley in Man- 
churia, but there seem no grounds for believing that 1t naturally habits 
any part of the Manchurian or other East Asiatic region. 
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\\VJ Probable Range BE Recorded Distribution 
Fic. 404.—Geographical Distribution of /elix hortensis Miiller 
in the Palearctic region. 
In the British Isles it is distributed throughout Great Britain, becoming 
in suitable districts increasingly more numerous and generally diffused 
towards the north. In Ireland, though probably existing throughout the 
country, it is said to display little variation in the north, and to be most 
plentiful and variable in the more southerly districts, and along the 
1 Monog. i., p. 394, f. 725. 
