Manchester Memoirs, Vol. Ixv. (192 1), No. 10 7 



Guide Bridge Canal near Dukinfield railway station have 

 shewn that :- — 



1. The correlation of each pair of measured axes (length, 

 width, and thickness) is high ; the coefficient of correlation 

 varies from +09288 in the case of length and thickness to 

 + 09628 in the case of length and width. 



,_, . . . ' . Width , Thickness 



2. 1 he variation in the ratios j -r and -= -j — 



Length Length 



is small. 



3. The coefficient of correlation of these two ratios has the 

 value + 0*5237, which is somewhat higher than in the case of 

 Sph. lacustre (Muller) and Sph. corneum (Linne). 



4. It is not possible from the data available to describe 

 with any great accuracy the development of form of the shell. 



The general features of the variation of all the species of 

 the genus will be discussed when dealing with Sph. rivicola. 



The University, Manchester. 

 Jan. 20, 1921. 



References. 



1. " Variation of Sphceria. 1. Sph. lacustre (Muller). " Manchester Memoirs, 



1921, 65, No. 8. 



2. " Variation of Sphceria. 2. Sph. corneum (Linn£)." Manchester Memoirs 



1921, 65, No. 9. 



