209 



FURTHER OBSERVATIONS ON THE OCCURRENCE 



OF MANGANESE IN LAND AND FRESH- WATER 



MOLLUSCA. 



BOYCOTT. 



{Contimied from page !j8). 



Similarly there is a certain amount of evidence that Limax 

 tenelliis, the other species of this group which gives uniformly 

 high results, is generally, but not always, found in specially 

 manganiferous places : — 



The circumstances of these two species, which characteristic- 

 ally, especially L. tenelliis, live in woods suggest that there 

 may. after all, be some connexion between their occurrence 

 and the prevalence of available manganese. Looking through 

 the data for the whole of the variable group D (slugs and 

 Hyalinia) , it is certainly curious that (i) all the high figures 

 have been found in specimens from wild places, and never in 

 those from loci which have come well under the influence of 

 civilisation ; (2) nearly all the figures from cultivated areas 

 are low; (3) some woods give low figures, but in no case can 

 those be exempted from a suspicion of being modern plantation, 

 at least these are the facts as far as I know the habitats in 

 detail ; material received from other collectors is in some 

 instances not sufficiently localised. Thus in the series of 

 Avion ater from 30 different localities, the 8 which are above 

 the mean (31) are from a beech wood in Buckinghamshire (47), 

 a wood in Cork (50), a wood near Nottingham (36), an oak 

 wood at Llanberis (55), a mixed oak wood in Devon (364), 

 an ash wood in Devon (40), a beech wood in Wiltshire ( 121), 

 and the New Forest (78) ; from gardens, fields, and hedge 

 banks in Herefordshire, Wiltshire, Devonshire, Down and 

 Buckinghamshire there are eleven ranging from less than i to 

 6. Similarly with Limax arhortim, the highest figures (96- 

 232) come from woods and from a sea-cliff in North Devon, 



1921 June 1 



