236 CHAPTER Iir 



The following facts may be regarded as indicators of late arrival with man of 

 Cepaea hortensis into North America: — 



(a) The restriction of area in North America to the sea-shore of the Northeast. 

 There is only one old, unlocalized inland record, from northern Vermont, by A. 

 Binney {vide Johnson, 1906, p. 74), which requires confirmation. In Europe (map, 

 fig. 29), Cepaea hortensis is not at all restricted to coastal regions, nor to districts 

 showing an oceanic climate. Attempts to explain its absence from inland localities 

 as due to unsuitable edaphic and other conditions (Johnson, 1906, p. 80; Pilsbry, 

 1939, p. 8) are not in the least convincing since the species in Europe shows no 

 tendency to fastidiousness in choice of soil; it cannot be termed "calciphile", 

 more than all shell-bearing snails are, though Pilsbry (I.e.) does so. The restricted 

 distribution in North America has no doubt historical reasons. 



(b) The frequent occurrence of Cepaea hortensis in North America on small 

 islands off the coast has been used as an argument against the theory of introduc- 

 tion. Actually, this argues in favour of the theory. Brooks & Brooks (1940, pp. 

 59, 61) found a couple of European snails (Limax marginatus Miill. and Vertigo 

 alpestris Aid.) on small, uninhabited islands off the coast of SE Newfoundland and 

 likewise regarded this as a sign of indigenous occurrence, but it is given a far more 

 natural explanation by the assumption that sailing vessels discharged their ballast 

 on these islands, especially at low tide, before entering the port of destination. As 

 mentioned above (p. 157), tipping of ballast into the sea was prohibited in old days. 



(c) The oldest record of living Cepaea hortensis from North America seems to 

 be from St. Pierre-Miquelon, in 1822 (Taylor, 191 1, p. 366); from Quebec in 

 1829, New England (Mass.) in 1837 (Johnson, 1906). Though this gives no evi- 

 dence as to time and place of a possible first introduction, it suggests the New- 

 foundland region as the primary immigration area. The species was also unmen- 

 tioned in two lists of New England shells from 1833 (according to Johnson, 1906, 



P- 73)- 



(d) A. Binney (according to Johnson, I.e., and Taylor, I.e.) observed that on the 



small Salt Island off Gloucester, Mass., Cepaea hortensis in 1837 occurred exclusively 

 in the unhanded variety, but in 1851 he reported that the banded variety was 

 "not uncommon" on the same island. This indicates an instability of the popula- 

 tion contradicting the idea of old age on the spot in question. The shell char- 

 acter mentioned has a hereditary base and the factor "unhanded" behaves as 

 a dominant (according to the well-known breeding experiments by A. Lang; 

 vide also Boettger, 1950). Apparently Salt island was originally colonized by 

 snails with unhanded shells, in part heterozygotes. 



(e) Cepaea hortensis, if native in North America, would display a quite unique 

 type of distribution. It would constitute the single Amphiatlantic animal species. 



