HUTTON : LIMN.liA PERECJEK M. SINISTKORSUM. 59 



though never very numerous at any time. I am afraid they are now 

 extinct in one of the habitats. 



I have never yet found a specimen of L. pereger m. sinistrorsum 

 or heard of any records of finds on a hmestone formation ; apparently 

 the most favourable habitat is a clay soil or sandstone formation ; a 

 pond with a clay-mud bottom, and Elodea canadensis, Callitriche 

 verna, Le/nna minor and L. irisuica for vegetation. Its molluscan 

 associates are Limncea auricularia, Planorbis corneals, F. umbilicalus, 

 sometimes F. carinatus, F. spirorbis, and L. sfagnalis, which is be- 

 lieved to be detrimental to the increase of most other mollusca in a 

 pond. In one habitat I have found it in association with Vivipaia 

 vivipara. 



From frequent observations and examination of habitats where 

 abnormal specimens occur, I believe soft water is most favourable to 

 the formation of abnormal freshwater shells. Mr. J. W. Taylor, in 

 his valuable Monograph, vol. i, p. 104 and p. 114, illustrates speci- 

 mens of F. carinatus m. sinistrorsutn, and other forms, from Leven- 

 thorpe Pastures, near Leeds, a habitat I have often visited. This 

 stream is of soft clay water, and is largely fed from the warm exhaust 

 of a pit-engine ; in that habitat abnormal shells were more frequent 

 than normal. 



On a Colony of Cochlicopa lubrica Miiller.' — It may be worth recording 

 ihal while on a ramble in East Knighton Wood, on the south side of Ashey Down, 

 near Brading, in the Isle of Wight, last August, I came somewhat unexpectedly 

 on a colony of Cochlicopa lubrica on the trunk of a good-sized beech. The mol- 

 luscs, about fifty in number, present a departure from the usual colouration of the 

 species, all of them tending more or less towards the form known as the var. 

 hyalina. Though only seven could strictly bear the name of that variety, the others 

 were nearly all very pale in hue. The snails were attached to crevices in the 

 bark, and some reached up as high as five or six feet from the ground. Though it 

 is not unusual to discover this species on beech trunks, I never before met with so 

 large a colony. The most notable feature about the habitat was that the surround- 

 ing ground was entirely devoid of green vegetation, so that apparently the molluscs 

 were compelled to find their sustenance on the bark which was thinly coated with 

 lichen and at the base with a little moss. Two or three Helix rotundata with some- 

 what eroded tests, which gave them a patchy-white appearance, were found on the 

 undersides of fallen pieces oi bough lying on the ground within the circuit 

 sheltered by the outspread limbs of the beech tree ; but no C. lubrica were to be 

 found anywhere but on the main tree-trunk itself. It would seem that this colony 

 of white or whitish C. lubrica may be due to the peculiar features of its habitat, 

 its isolated position limiting and restricting the range of its feeding ground to the 

 scanty vegetation on the tree-trunk. — S. Spencer Pearce {Read before the 

 Society, Oct. 13th, 1917)- 



