20 Proceedings of the Royal Irish Academy. 



concurred with Professor Moi-se's opinion, while the Eev. !Mr. "Winkley 

 even suggested that Hdix hortensis arrived in North America before the 

 advent of the Glacial period. With the latter theory, Mr. Johnson, another 

 conchologist, expressed his agreement; and it is to his paper that I am 

 indebted for the above-mentioned information.' 



The only one who adhered to the introduction theory was Dr. Pilsbry. 

 He even aigued in favour of artificial importation by the ancient Vikings 

 during their supposed visit to the American coast in the eleventh century. 



All doubts as to the claim of Helix hortensis being an indigenous 

 American species are now set at rest through the discovery by Dr. Dall of 

 the shell of this snail in undoubtedly Pleistocene deposits in the state of 

 Maine.' Moreover, the species is now known to inhabit a much greater 

 area than was formerly supposed ; for it has been collected in Labrador, 

 Newfoundland, Prince Edward Island, and many other small islands where 

 it could not possibly have been brought by man. It may therefore be 

 considered as definitely established that Helix hortensis reached America in 

 Pleistocene or Pliocene times without human intervention. That greater 

 facilities may have existed for tlie occasional transport across the Atlantic iu 

 those remote times than obtain at present might still be urged iu accounting 

 for its presence in America. Such an hypothesis, however, is unsupported by 

 any testimony, while the view advocated that it travelled across a laud-bridge 

 to America is corroborated by other distributional facts, and meets with 

 the approval of many zoologists. 



The discovery of Helix hortensis in Greenland is an important factor iu 

 favour of the land-connexion theoiy. That this species should have survived 

 the Glacial period in that country need not surprise us; for several other species 

 of land and freshwater molluscs certainly must have done so. Flanoi-bis 

 arctica, Limnaea Vahli, L. Wormskioldi, Succinea groenlandica, Vitrina 

 nngelicne, Pupa Hoppii, and Ccmitlus Fabricii are almost all confined to 

 Greenland, and no doubt originated there in Pre-GIacial times. 



I feel sure many other European terrestrial Invertebrates with a range 

 similar to that of Helix horteiim are found in America. I know of such 

 among the earthworms and woodlice, but there is no need to add to the 

 above examples. 



Before summarizing the results of these investigations into the evidences 

 of a former land-bridge between northern Europe and North America, I wish 

 to mention the opinions of a few naturalists besides those referred to who 



' Johnson, C. W., " Distribution of Hrliz hortrniu," p. 73. 

 » Dall, W. H., "Land and Fieshwatcr MoUuaks," p. 20. 



