Manganese in Land and Fresh Water Mollusca. 73 



•case of Pot. crispus, natans and densus, the first figure refers 

 to fresh shoots, the second to older, discoloured portions. 

 The sinter was most obvious in the specimens of Pot. crispus, 

 lucens, and especially perjoliatus, and the fact that the figures 

 for these species are on the whole rather low suggests that it 

 is not a very important factor in raising the content in manga- 

 nese. I daresay that the prodigious amount of manganese in 

 the hydrohypnum was largely a surface deposit or entangled 

 precipitate which was not removed by moderate washing and 

 squeezing in water, 1 but in any case an animal feeding among 

 it would probably pick up a good deal. 



Taking the figures in a general way, algse and such like 2 

 (but not fungi 3 ) seem to have a good deal more than the higher 

 plants, and the suggestion that the manganiferous snails 

 (Hyalinia, Buliminus) eat specially large amounts of these 

 is obvious. Note, too, that Scharft 4 classes L. maximus, 

 arborum, Arion subfuscus, minimus and Geomalacus as the 

 slags which characteristically feed on non-chlorophyllaceous 

 plants. It is rather curious that waHr snails have much less 

 manganese chat the manganiferous land species, considering its 

 much greater abundance in water plants. 



Summary. 



The proportion of manganese in the bodies of land and 

 fresh-water mollusca varies widely in different species ; there 

 are exceptionally large amounts in Anodon, Unio, Buliminus, 

 Hyalinia, Ancylus and Limax (partly), while Sph cerium and 

 the Helicidce have comparatively little. 



I am very much indebted to a number of friends for kind^' 

 help, and Miss M. Boycott, Mr. Charles Oldham, the Rev. Dr. 

 Cooke, Miss Hopton, Mr. J. W. Jackson, Mr. R. Standen, 

 Mr. W. D. Roebuck, Mr. J. W. Taylor, Mr. H. Beeston and 

 Dr. E. J. Salisbury have supplied most useful specimens and 

 other assistance. It is evidently desirable that specimens from 

 a wider range of localities and habitats, especially from the 

 north, should be examined, and I should be particularly glad 

 of help in clearing up the positions of Limax arborum, L. sub- 

 fuscus, L. cinereoniger, H . lapicida, Planorbis corneus, Paludina 

 and M. margaritifera. I have also been unabie to gain an}' 

 information about the occurrence of Crenolhrix manganifera 

 ir tnis country : an account of it is given by D. D. Jackson. 5 



1 This is supported by the fact that two different samples gave widely 

 varying results, viz., 890 and 489. 



2 My botanical identifications are terribly inadequate : I hope someone 

 better equipped may investigate the matter. 



3 I judge this from my own analyses, and the summary statement of 

 Jadin and Astruc, Combtes Rendus, Vol. CLV. (1912), p. 406. 



4 Set. Trans. Roy. Dublin Soc, Vol. IV. (1891), p. 513. 



5 Trans. Amer. Micro. Soc, Vol, XXIII. (1902), p. 31. 



1917 Feb. 1. 



