212 
ORIGIN OF LIFE IN AMERICA 
the latter belongs to the same great family Helicidae as the 
European Arianta, but that otherwise it is quite unrelated 
to it. He places the Californian forms, therefore, into the 
genus Epiphragmophora, contending that its nearest rela¬ 
tions are the Helices of Japan. In another place (p. 46) he 
adds the remark that it is unnecessary to throw land bridges 
across the depths of the Atlantic and Pacific Oceans to account 
for the distribution of Helices. Such hypotheses, he thinks, 
are contrary to many facts indicating that such groups of 
snails as are common to America and Europe have radiated 
from an Oriental centre westward to Europe and eastward, 
by way of a former Bering Strait land bridge, to America. 
Yet Dr. Pilsbry’s conclusions, as I have already mentioned, 
are contested by Dr. von Ihering likewise on anatomical 
grounds. Although Dr. Pilsbry maintains that his opponent 
bases his deductions on figures and not dissections (p. 195), 
Dr. von Ihering, in a recently published paper, again insists 
that, after having made a careful anatomical investigation of 
Arianta, (or Helicigona as he calls it,) and the American 
Epiphragmophora, he could perceive no difference worth men¬ 
tioning between the two. Hence Dr. von Ihering’s * opinion 
is that the American Helices, which are now generally known 
under the name of Epiphragmophora, and which are entirely 
confined to the Pacific coast of America, possess their nearest 
relations not in Asia but in western Europe. 
Let us take another group, that of the well-known Euro¬ 
pean family of slugs, the Arionidae. In 1896 Messrs. Pilsbry 
and Vanatta f showed by anatomical investigations that the 
American slugs Ariolimax and Aphallarion belong to this 
family. Later on the same writers added the genera 
Anadenulus, Hemphillia, Hesperarion and Prophysaon to 
this list. The whole of this great assembly of Arionidae 
is quite confined to the Pacific region between British 
Columbia and southern California. No other slug of this 
family has as yet been discovered anywhere in the New 
World, except one or two European species in the north¬ 
eastern States, which may either have been introduced 
* Ihering, H. von, “ System der Heliciden,” p. 422. 
t Pilsbry, H. A., and E. G. Vanatta, “Eevision of North American 
Slugs.” 
