14 Manganese in Land and Fresh Water Mollusca. 



E. obscura. Beech woods, Hampden 85 ; Cranham 75 ; 



hedge-bank, Aldenham, 81. Mean 80. 

 Clausilia laminata. Monk's Risborough, Bucks, (beech wood) 



6 ; Aldenham (hedge-bank) 10. Mean 8. 

 Saccinea putris. Doward, Hereford 6. 



S. elegans. Hereford 3 ; Long Lane, Middlesex 3. Mean 3. 

 Ancylus fluviatilis. Aldenham 21. 

 Limncea auricularia. Aldenham, two loci, 2, 3. 

 L. peregra. Aldenham (a) ponds, nine loci, 1, 2, 2, 3, 3, 4, 5, 



7, 10 ; (b) streams : — five loci 2, 3, 4, 4, 4. Mean 4. 

 L. palustris. Aldenham (a) ponds, three loci 2, 2, 3 ; (b) river, 



trace. Mean 2 ca. 

 L. stagnalis. Aldenham (a) ponds, eleven loci, 1, 1, 2, 2, 4, 



5> 5. 5> 6, 9, 29 ; (b) river 2 ; Alderley Edge, Cheshire 6. 



Mean 6, or (without exceptional case) 4. 

 Planorbis corneus. Aldenham 2 ; Hereford 18. Mean 10. 

 PL complanatus. Aldenham, three loci (ponds), 2, 3, 4. Mean 3. 

 Physa fontinalis. Aldenham, two loci (streams), 3, 8. Mean 6. 

 Ph. hypnorum. Aldenham, trace. 



Gastropoda prosobranchia. 



Bithinia tentaculata. Aldenham, two loci o*8, i-i. Mean 1. 

 Pomatias elegans. Aldenham 1-2, i-i ; Monk's Risborough ; 

 trace. Mean o«8 ca. 



Pelecypoda. 



Unio pictorum. Aldenham (lake) shell, 37 mm., 27 ; 45 mm., 



36 ; 75 mm., 19. Mean 27. 

 Anodonta. Aldenham (lake) shell, 65 mm., 24; 100 mm., 34 ; 



120 mm., 113 ; Barton (Canal), Lanes., 80 mm., 27 ; 



Birmingham no mm., 56, 96 ; locality unknown 35 mm., 



24. Mean 53. 

 Sphcerium corneum. Aldenham, four loci (three ponds, one 



river) nil. 

 Sph. lacustre. Aldenham, four loci (ponds) nil. nil, nil, trace. 

 Pisidium amnicum. Aldenham, nil. 



Putting these results together, it is evident that the species 

 examined fall into several groups as regards their content in 

 manganese. 



(a) Taking first the land snails, the helicids show little, 

 ranging from obvoluta, barbara, hispida, rufescens with hardly 

 any to nemoralis, aspersa, granulata and pomatia, which show 

 up to 2 parts per ten thousand : the position of lapicida is 

 uncertain, specimens from two loci in the Forest of Dean 

 showing as much as 6 and 12, while others from the Cotswolds 

 and Chilterns gave only a trace. The Zonitidse, on the other 

 hand, give uniformly high figures, which are the more reliable, 

 as specimens have been examined from a wider range of 



Naturalist, 



