8 W. E. Alkins and M. Cook — Variation of Sphceria 



™, . . . . Length , Thickness 



2. I he variation in the ratios TTr . TV and — ? = — 



Width Length 



is small, though it exceeds that previously found for Sph. 

 lacustre (Miiller). 



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

 value + 045, which agrees closely with that found in the case 

 of Sph. lacustre. 



It is not possible from the data available to describe the 

 development of form of the shell. 



Metallurgical Department, The University, 



Manchester. 



REFERENCES. 

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



1921, 65, No. 8. 

 2. Ibid., p. 2. 



