80 THE NAUTILUS. 



England coast, and being found in pre-Columbian kitchen-midden 

 deposits, cannot be regarded as a recent immigrant. Possibly it may 

 be the sole survivor of that Viking incursion in the eleventh cen- 

 tury." Rev. Henry W. Winkley, in an interesting article, " Helix 

 hortensis in New England" (Nautilus, XVII, p. 121, 1904), sug- 

 gests that it is a survivor of the pre-glacial period. When we con- 

 sider its present distribution and power to withstand even the 

 climate of Iceland, this seems to be the only solution of the problem, 

 which is further strengthened by its discovery in the Pleistocene by 

 Dr. Dall (loc. cit.), wlio says : " The wide distribution of the species, 

 often on uninhabitable islets off a coast little frequented, and its 

 presence, which I have verified, in the glacial Pleistocene of Maine, 

 tends to confirm the view that it is a prehistoric immigrant if an 

 immigrant at all." 



The question Avhich now arises is this : Why does Helix hortensis 

 continue to occupy the outer islands and headlands and not spread 

 further inland ? I think this can be quite readily explained, as far 

 as the New England coast is concerned, by taking into consideration 

 the geological character of the coast and the conditions most favor- 

 able to the life of land niollusks. The New England coast is com- 

 posed almost exclusively of granitic rocks, or, on Cape Cod, of sand 

 and gravel, both very unfavorable geological conditions for mollusca, 

 owing to the absence of lime ; even the more common species of the 

 eastern United States are comparatively few on the coastal area. 

 Again, the atmospheric conditions even slightly removed from the 

 outer shore line are very different from the islands and headlands, 

 continually bathed by the ocean's spray. These barren locations 

 make up in lime and moisture what they lack in vegetation; the 

 islets are also probably much more free from mice, rats and forest 

 fires, which on the mainland destroy large numbers of snails. Poly- 

 gyra albolabris and Pyramidula alternata are much more abundant 

 on the islands than on the adjacent mainland, nor do these remarks 

 apply only to the New England coast. The sandy pine and scrub 

 oak barrens of southern New Jersey are void of land shells, while on 

 the islands separated from the mainland by a wide expanse of salt 

 marsh, and numerous creeks and bays, Polygyra albolabris var. 

 maritima is quite abundant. The distribution of hortensis along the 

 broad estuary of the St. Lawrence is undoubtedly due to favorable 

 physical conditions. 



