138 Bovcott: Manganese in Land and Fresh-ivater Molltisca. 



harbovir tht whole series of species which one would desire. 

 If Umax, Hyalinia, Helicella and Helix in their several sorts 

 would all live together in one habitat, a direct answer could 

 be obtained ; but they do not. We have only a few possible 

 comparisons of helicids with more manganiferous species. 

 Thus H. rufescens living with Buliminus montamis (78) in 

 beech woods in Buckinghamshire or Gloucester keeps to the 

 same low figure as it does in hedge banks and gardens elsewhere. 

 Similarly B. obscurus always maintains a high level whether it 

 lives with Limax tenelhis or Helix aspersa. P. rotundata 

 from the most manganiferous locality I have examined gave 

 only 4 as against a general average of 2. In the only place 

 in which I have been able to find Helix nemoralis and H. 

 hortensis living alongside Limax niaximus and L. arborum (a 

 Wiltshire beech wood) the whole series of slugs and snails 

 gave the low figures normal for the latter. Zonitoides excavatus 

 gives consistently high results and has an average nearly twice 

 as great as any other species. From two of the six localities 

 (oakwoods at Bodmin==388, and Leeds=ii6) I have no other 

 species. The other four loci give : — 



All these localities were, as usual, woods on non-calcareous 

 soils and of oak or oak mixed. The figures show that excavatus 

 has in each case accumulated a great deal of manganese, 

 that there is a distinct tendency for other species from the 

 same woods to give high, but by no means maximal figures, 

 but that it may be found in places where the other sorts give 

 no more than average figures. It would be interesting to 

 know what Hygromia fiisca does when it lives alongside 

 Z. excavatus, but I have been unable to obtain specimens. 



(To be continue J ). 



