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, "Revision of North American 

 Slugs." 



