o4 Notices of Memoirs—Dr. R. F. Scharff— 
Greenland had generally been attributed to a recent human intro- 
duction; but it has been taken in several different localities, and 
we must, I think, look upon it as an indigenous species. During 
the year 1864 Professor E. 8. Morse discovered the shell of this snail 
among ancient ‘kitchen-middens’ on some of the islands off the coast 
of Maine. This fact led him to consider that the snail had wandered 
along some ancient coastline from the Old World across the North 
Atlantic. Dr. Binney, and more recently Professor Cockerell, con- 
curred with Professor Morse’s opinion, while the Rev. Mr. Winkley 
even suggested that Helix 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.? 
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 if 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 JZelix hortensis reached America in Pleistocene or 
Pliocene times without human intervention. 
The discovery of Helix hortensis in Greenland is an important factor 
in favour of the land-connexion theory. 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. Planorbis arctica, Limnea Vahli, L. Wormskioldi, 
Suceinea grenlandica, Vitrina angelica, Pupa Hoppirt, and Conulus 
Fabricti are almost all confined to Greenland, and no doubt originated 
there in Pre-Glacial times. 
Of all the theories which have been advanced in explanation of the 
occurrence of identical species on both sides of the Atlantic Ocean, 
only the following three have met with wide approval :— 
1. Migration from Europe across Asia and a Bering Strait land-bridge to 
America or vice yersa. 
2. Occasional transport by birds across the Atlantic Ocean. 
3. Migration across a direct Atlantic land-connexion. 
If we consider the zoological evidence alone, namely, the absence of 
Helix hortensis from Asia and Western America, the distribution 
of the Perches and the freshwater Pearl-Mussel, and that of the 
freshwater Sponges, the first of the three hypotheses is scarcely 
applicable to these instances of distribution, and does not, therefore, 
explain the presence of identical species on both sides of the Atlantic 
in a satisfactory manner. 
As regards the supposed conveyance by birds of seeds and in- 
vertebrates across the same ocean, the second theory must be 
1 C6. W. Johnson, ‘‘ Distribution of Heli hortensis”’?: Nautilus, 1906, xx, p. 73. 
2 W. H. Dall, ‘‘Land and Freshwater Mollusks’’: Harriman Alaska Exped., 
1905, xiii, p. 20. 
