253 



NOTES ON CHESHIRE LAND AND FRESH- 

 WATER MOLLUSCA. 



CHAS. OLDHAM, F.Z.S. 



The following notes are intended to supplement a paper 

 entitled ' The Land and Freshwater MoUusca of Cheshire/ 

 which appeared in ' The Naturalist ' for 1896 (pp. 109-128). 

 During the past twelve 3'ears I have had few opportunities 

 for collecting shells, but, as I am no longer living in Cheshire, 

 it seems desirable to add to my previous record such notes on 

 the less common species as I have. With these I have incor- 

 porated information published in ' The Naturalist,' the ' Journal 

 of Conchology,' and Mr. J. W. Taylor's ' Monograph of the Land 

 and Freshwater Mollusca of the British Isles,' and notes on 

 specimens in the collections of Mr. B. R. Lucas, and the Rev. 

 H. G. Barnacle, to both of whom 1 am indebted for information. 



Of the twelve species mentioned in the following notes, which 

 were not included in my list,* six are indigenous to Britain, but 

 only three — Acanthinida lamellata, Vallonia excentrica and 

 Vertigo pusilla — to Cheshire. Testacella maugei, T. halio- 

 tidea and Vitrea draparnaldi are, locally, only found in and about 

 gardens, and are, obviously, introduced forms. Milax sow- 

 erhyi and M. gagates, although more firmly established than 

 these three, have, in my opinion, no better claim to be considered 

 as native in Cheshire. Planovhis corneus, Vivipara contecta 

 and, probabl}^, Dreissensia polymorpha and SphcBrium pallidum 

 belong to the same class. Opeas goodalli and Subulina odona, 

 tropical forms, occur only under highly artificial conditions in 

 hot-houses, but are mentioned as a matter of general interest. 

 During the past ten years four alien species — Planorbis dila- 

 tatus, Physa heterostropha, Paludestrina fenkinsi and P. 

 taylori — have been detected in the local canals. The first two 

 are American species, but whence the last two reached this 

 country is unknown. Planorhis dilatatus is hardly likely to 

 become permanently established except in the vicinity of cotton- 

 mills, where effluents of warm water provide the temperature 

 necessary for it, but Physa heterostropha is bound by no such 

 limitations, and Paludestrina jenkinsi, which has displayed 

 in Cheshire as elsewhere in Britain an extraordinary capacity 

 for colonization, is already widely diffused. Paludestrina 



* These are indicated by an asterisk. 



1908 July I. 



