LAND AND FRESHWATER MOLLUSCS OF INNER HEBRIDES 21 



basaltic islands Ulva and Eorsa, on both of which the only 

 conspicuous snail is Helix neinoralis. This species, on the 

 other hand, we did not see either on lona or on Innis 

 Kenneth. It must be at any rate rare on these islands, on 

 which it has been perhaps entirely replaced by H. aspersa, 

 the environment not supplying provender or shelter for more 

 than one species of large snail. Helix aspersa and Helicella 

 itala are both Mediterranean species, and attain a much 

 larger size in the south of Europe than they do in Scotland, 

 where they are approaching the northern limit of their range. 

 H. aspersa grows still larger in Algeria than it does on the 

 Riviera. Even as far north as Edinburgh it is found on 

 various soils, and it is abundant on the Bass Rock in the 

 Firth of Forth. Probably its foothold in the Hebrides is 

 precarious, and it is only able to survive where conditions 

 are particularly favourable. I have noticed in Algeria and 

 the Alpes-Maritimes that it is distinctly xerophilous in 

 habit, and probably the damp peaty soil of Ulva and Innis 

 Kenneth is antagonistic to it. It is evidently indifferent to 

 cold, for I have seen large shells in the Kabyle mountains 

 over 4000 feet above sea-level. Certain other species, 

 notably Pupa uiubilicata and Clausilia bidentata, are very 

 much more abundant on lona than on the other islands, 

 apparently because they find a particularly favourable 

 habitat among the ancient ruins. 



It is somewhat remarkable that no less than five species 

 of freshwater molluscs, and one inhabiting brackish water, 

 were found on the smaller islands. None was obtained from 

 the pools on the hill-tops, but in the little streams on Ulva, 

 at different parts of their course, six species were found. 

 Even on Eorsa, on which there are no real streams, one 

 species [Liinncea truncatuld) was taken in a small pool 

 caused by drippings from the cliffs. On Innis Kenneth 

 three species were collected in small springs. The species 

 found in the hill streams of Ulva were Liinncea peres-ra 

 L. trtmcatiila, Attcylus flitviatilis, Pisidiuni casertaiium and 

 P. personatuvi. In the springs on Innis Kenneth the Ancyhis 

 and P. persouatuni were absent. No freshwater specimens 

 were collected on lona, but two, L. peregra and P. nitiduvi, 



