io W. E. Alkins — Variation of Sphceria 



_, . . . , . width , thickness . 



2. The variation in the ratios . r and —. -r- is 



length length 



remarkably small. 



3. The correlation between these ratios is low ; the co* 

 efficient of correlation is slightly greater than two-fifths ; but 

 the presence of two shells, abnormal in shape possibly on 

 account of an injury sustained at an early stage of growth, 

 increased this to practically one-half for the whole series. 



4. The data are not sufficiently exhaustive to furnish any 

 reliable information as to the actual development of form of 

 the shell. 



The writer wishes to express his cordial thanks to Mr. 

 W. Cartwright for his valuable assistance in collecting and 

 cleaning the shells, and to Mr. J. Harwood, M.Sc, for his 

 help in recording the measurements. 



Metallurgical Department, The University, 



Manchester. 



Appendix. 

 Note on the Pisidia associated with Sph. lacustre. 



The author has received from Mr, A. W. Stelfox, M.R.I.A., 

 the result of his examination of the Pisidia from the station 

 where the Sph. lacustre were taken. Mr. Stelfox reports (Jan. 

 17th, 1921) : — 



P. nitidum, Jenyns : One only ! A fine healthy adult, but 

 not a very typical shell. 



P. milium, Held : Thirty-five specimens ; not quite so 

 rectangular as usual ; all adult but three. 



