6 W. E. Alkins & J. HARWOOD — Variation of Sphceria 

 TABLE V. TABLE VI. 



Distribution of Wldtl * Ratio. 

 Length 



Distribution of Thickness Ratio. 

 Length 



w 





w 





w 





T 





T 





L 



No. 



L 



No. 



L 



No. 



L 



No. 



L 



No. 



1*31 



2 



1-39 



53 



1-46 



29 



0-55 



1 



0-63 



67 



1-32 



3 



1-40 



48 



1-47 



10 



•56 



4 



•64 



45 



1-33 



3 



1-41 



51 



1-48 



9 



•57 



13 



•65 



33 



1-34 



7 



1-42 



56 



1-49 



3 



•58 



32 



•66 



28 



1-35 



9 



1-43 



58 



1-50 



1 



•59 



40 



•67 



25 



1-36 



12 



1-44 



43 



1-51 



2 



•60 



56 



•68 



8 



1-37 



30 



1-45 



35 



1-52 



1 



•61 



63 



•69 



7 



1-38 



35 











•62 



77 



•70 



1 



In spite of the fact that the class-interval has been taken as 

 low as o*oi, there is only one slight irregularity (between 1*38 



and 1 '40 in the -. r distribution. This in itself is con- 



^ length 



vincing evidence of the homogeneity of the species — which 



is indeed borne out by every other character to which any 



attention has been paid. 



,i\ r- 1 *- 1 47 d *• Width , Thickness 



(f) Correlation of tfte Ratios T r and — r nr . 



yj/ Length Length 



An extended correlation table for the two ratios which have 



been under discussion is given in Table VII. Though the 



correlation is by no means precise, there is still a definite 



tendency for high values of one ratio to be associated with 



high values of the other. The coefficient of correlation has 



the value + 05327, and is thus rather higher than was found 



to be the case in the other two species. The equations of 



regression are : — 



(a) '* = 1005 +0-657 I » 



with the standard error ± 0*0294; 



(b) 



T _ 



W 



001 1 + 0-432 Ji, 



L -Li 



with the standard error ± 0*0239. 



Summary. 



Measurements of length, width, and thickness of a series of 

 Sphcerium pallidum, Gray (five hundred) from the Ashton and 



