328 Scientific Proceedings, Royal Dublin Society. 



of L. truncatula found upon the bare rock-faees of the sandstone clifE of 



Croaghmore, which faces the Atlantic on the west of the island. The snail 



is found up to nearlj- 1,000 ft. Taylor (1920) does not include L. truncatula 



among the moUusca found in the low-lying district of Audruicq, in Picardy, 



and comments upon the absence of limestone. Kendall (1921) records the 



finding of L. truncatula in the Oundle district in river marsh— rush-grown 



shallows and moist river margins, also in small streams, but not in "natural 



marsh" — an extensive tract of boggy ground with common rush, cotton grass, 



bog bean, marestail, and peppermint. 



Through the kindness of Sister Monica Taylor, Mr. G. L. Walton, Miss K. 



Carpenter, Mr. T. H. Taylor, and Mr. W. M. Temple the authors have been 



provided with certain samples and notes concerning the distribution of these 



snails in Scotland, "Wales, and Yorkshire, as well as near Plymouth. The 



1 ^ 



values for pH = log jr ^^e recorded for these soils or waters, as are also 



the electrical conductivities of the waters measured at 0° C, at which 

 temperature N/100 potassium chloride has the value 0-00078, and was used 

 to standardise the cell. 



The data presented in the table opposite are obviously not as numerous 

 as could be desired, but are put on record and discussed now, as the subject 

 is foreign to the authors' general line of work, and it is not their intention 

 to pursue it further. The crosses given in the table denote a rough attempt 

 at giving an idea of the relative abundance of the two species. 



It must be explained that pH 69-1-6, for example, does not mean that 

 the value lay between those limits, but that when examined it was pH 69, 

 and when the water was thoroughly well aerated and the free carbon dioxide 

 was reduced thereby so as to be approximately in equilibrium with the air, 

 the pH value then rose to pH 7-6. The condition of soft water at pH 69 is 

 tlierefore very different from that of hard water at the same lyH value, for 

 though the reaction is the same the hard water is charged with a great excess 

 of carbon dioxide above the equilibrium value, and is correspondingly poor 

 in oxygen, whereas a soft water at this pH value may be thoroughly well 

 aerated. It is obvious that the oxygen content of water is of great biological 

 importance. The change in pH value produced by aeration may, therefore, 

 be taken as giving a rough idea of the degree to which the water is satiTrated 

 with oxygen. 



The electrical conductivity of the water gives a measure of its salt content, 

 which, when dealing with normal natural waters, may be taken as roughly 

 proportional to its hardness. Hard water has a conductivitj^ of 270-290 X 10"", 

 whereas a very soft water like the Plymouth town supply from Burrator 

 reservoir, on Dartmoor, has a conductivity C = 26-28 X 10"", with a i)H 

 value of 64 to 68 according to season ; these values are unaltered by aeration, 

 but a spring water at pH 68 and having C = 270 X 10"'^ rises to over pH 8 

 on aeration. 



On inspecting the table it may be seen that, though the records are not 

 numerous, they may be taken as typical of districts of some size. As regards 

 the conductivity a wide range may be noted; this indicates a yet wider range 

 in "hardness," for even the soft watei's of the E. Ystwyth and its neighbours 

 liave C = 39-72 X 10"'', the Aberystwyth* town supply being as low as 

 C = 19 X 10-°. L. truncatula has been found in water having conductivity 



■ The authors are indebted to Miss K. Carpenter for these samples. 



