The land snail formerly known as Helix aspersa* displays a wide variation in the size of its adult shell. The smallest individuals have been called Helix aspersa minor, while the largest ones are known as Helix aspersa maxima. Taylor (Land & Freshwater Mollusca of the British Isles, 1914) gave the shell diameters of typical individuals as about 35 mm, the smallest ones as 20-28 mm and the largest ones as 40-48 mm. It is not known if these variations represent distinct species, subspecies or simply the results of environmental differences arising from phenotypic plasticity of the shell dimension.
Here are 2 adult shells of Helix aspersa from the same locality. The diameter of the shell on the left is 35.1 mm and that of the one on the right is 44.0 mm.
Below is a histogram showing the distribution of the maximum shell diameters of 35 empty shells I collected in an area that was roughly 140 m x 140 m.
The 3 shells with diameters larger 40 mm may represent Helix aspersa maxima. I will write more on this subject in future posts.
*Now called Cornu aspersum, etc.