82 H. GKOTES TEKTIGO MOTJLrNSIANA IN HEETFOEDSHIEE. 



plants which live in very watery places. Vertigo Moulinsiana 

 usually occurs in the greatest numbers at some distance up the 

 growing leaves and stems of the plants, while V. antivertigo, its 

 companion, seems to prefer the decaying leaves which have fallen 

 into the water, and is found only just above the surface of it. It 

 is rather remarkable that this shell should not have been previously 

 found or noticed in England ; and I can only account for it by 

 supposing that most conchologists have been afraid of venturing 

 into these very marshy places, which require tall fishing boots to 

 go into them with impunity ; otherwise a good wetting is inevitable. 

 I hope, however, that these remarks will not deter those members 

 of this Society who may be induced to take an interest in concho- 

 logy from searching similar places in other parts of the county ; 

 because I feel certain that this, at present, very rare shell will be 

 found to be much more widely distributed than is generally sup- 

 posed. It will be seen that the localities which I have mentioned 

 show its existence in the three great divisions of southern and 

 eastern England, viz. the tract of Hampshire which drains into the 

 Channel, the Thames watershed, and the Ouse district ; and this is 

 a mollusk whose distribution would necessarily be much influenced 

 by river-systems. 



There is one other point suggested by V. Moulinsiana, and that 

 is as to the effect of what Darwin has called in- breeding, in i-efer- 

 ence to which he explains the small size of animals which occur on 

 small islands at a distance from the mainland. I noticed that 

 the specimens of V. Moulinsiana which I last found were much 

 larger than those from the locality in which I first discovered it ; 

 and I think it possible that this may in some degree be referable to 

 the isolation of the first- mentioned locality, which was a small 

 boggy marsh, with apparently no stream flowing in or out of it, 

 and where a few specimens only could be detected ; on the other 

 hand, these specimens were somewhat weather-worn at the apex, 

 which would seem to point to the somewhat exposed position as 

 having some influence on the size of the shells. I think that it is 

 well to call the attention of naturalists to this question ; and I 

 think it would be desirable to examine specimens of water-loving 

 animals, which cannot traverse dry tracts, when occurring in small 

 isolated localities. In investigating such questions it is necessary 

 to consider very carefully the physical conditions of the habitat, as, 

 for instance, with regard to a water-loving mollusk, a drier locality, 

 or a great altitude, usually results in smaller specimens. In the 

 case before us the Hampshire marsh is very little above the river- 

 level, and when my brother visited it in the middle of the summer 

 he found no appreciable difference in the amount of water as com- 

 pared with that at Easter when we first collected the shells. 



