Atkins and Lebour — Ilt/drogen Ion Concentration of the Soil. 237 



Wexford is in part similar, Init contains, lli^e Dublin, a tract of limestone. It 

 seems probable that the absence of these three species from Wicklow is not 

 due to want of complete investigation, as Stelfox (1912) records for Dublin, 

 Wicklow, and Wexford, 96, 73, and 80 species for 1910, which have onlj- 

 been increased to 97, 74, and 87 in Eoebuck's list nine years later. Moreover, 

 Bathyomphalus {Planorbis) contortus is found in every other county in Ireland 

 according to Stelfox. There is, however, a discrepancy as regards records for 

 V. piscinalis, the species being listed by Stelfox as present in Wicklow, though 

 not in Roebuck's list. It must at least be a rarity in Co. Wicklow. 



One of the writers collected MoUusca at Dalbeattie, Kirkcudbrightshire, 

 where the rock is chiefly grey granite. Very few occurred on the granite, but 

 about two and a half miles from Dalbeattie, on the Palnackie road, near Munches, 

 where the rock was basalt, the snails were strikingly numerous. The following 

 is a list of those taken from near the road where the basalt begins : — 



Helix nenwralis juv. 



Arianta arhustorum juv. 



Pyramidula rotundata, many. 



Acanthinula aculeata, common among fallen leaves. 



A. lamellata, common among fallen leaves. 



Functum pygmacum, common among fallen leaves. 



Hyalinia excavata, many. 



H. cellaria, fairly common. 



//. crystallina, common. 



H. nitidula, fairly common. 



H. alliaria, common. 



H. pura, common. 



Euconulus fulv'us, common. 



Vitrina pellucida, a few. 



Pupa umbilicata, common. 



Sphyradium edentula, very common. 



Spliyradium edentula v. substriata, common. 



C oclilico'pa lubrica, common. 



Balea perversa, on walls, common. 



Acme lineaia, one, among leaves. 



Carychium minimum, very common. 



Also the following slugs were present : — Arion hortensis, Agriolimax agrestis, 

 common, A. laevis, common. 



It may be pointed out that soil over granite is normally mai'kedly acid, 

 since this Tock gives off inappreciable amounts of alkali to neutralize plant 

 remains. With basalt it is, however, otherwise, for it has been found that while 

 a weathered basalt boiled with distilled water gives iisually a slightly acid 

 solution, yet a fresh basalt surface may quickly yield sufficient alkali to give a 

 reaction of pE 80. Out of eight basalts tested, on further boiling one remained 

 acid, pH 5-4, six were at p// 70-7-3, and one at pll 83. It is highly probable 

 therefore that the situation where snails were plentiful over basalt was markedly 

 less acid than the granite region. It was most probably slightly acid or even 

 almost neutral. The species found notably in the alkaline region were absent 

 from the basalt, viz., H. virgata, H. caperata, H. itala, and Hygromia striolata. 

 H. hispida was also absent, but species of Hyalinia, H. pura, H. (Euconulus) 

 fulva and H. alliaria, known to occur even on highly acid soil, were present. 



While the authors feel convinced that the acidity or alkalinity of a situation 

 is an important, and often a dominant, factor in limiting the distribution of 



