118 A First Studij of Natural Selection in ClausUia laminata 
TABLE II. 
Mean Length of Peripheral Radius, and Mean Angidar Distance, of each group 
of measures in 100 half -grown Clausilia laminata. (Every mean value 
determined from 100 observations, unless otherwise stated.) 
Mean Angular Distance 
from Standard Columellar 
Radius 

Mean Length of Peripheral Eadius 
- 11-31214 X 180° 
0-4808 (50 observations) 
- 10-45494 X 180° 
0-6482 (97 „ ) 
- 9-45872x 180° 
0-9132 
- 8-45872 X 180° 
1-1446 
- 7-45872 X 180° 
1-4154 
- 6-45872x180° 
1-7021 
- 5-45872x 180° 
2-0367 
- 4-45872x 180° 
2-3770 + 0-00950 
- 3-45872x180° 
2-7683 + 0-01035 
- 2-45872x180° 
3-1838 + 0-01043 
- 1-45872 x 180° 
3-6489 + 0-01137 
- 0-49560x180° 
4-1457 + 0-01205 (91 observations) 
+ 0-49048 X 180° 
4-6952 + 0-01489 (62 „ ) 
It is difficult to compare the vahies of the mean radii directly in young and in 
adults, because the mean angular distance is not the same in corresponding groups 
of measures. The mean angular distance is however so close to J-ffi° in each case, 
that the value of the ordinate at that point, found by linear interpolation, will 
have a probable error only slightly greater than that of the entries in Tables I. 
and II. The necessary interpolations have been performed in Table III., the mean 
radius for the lowest (youngest) group of measures of the half-grown individuals 
being left unchanged, and the corresponding adult radius found by interpolation. 
TABLE IIL 
Mean Peripheral Radius at Corresponding Points on the Spiral q/" 100 Young 
and 100 Adidt Clausilia. 
Angular Distance 
from Standard 
Columellar Radius 
in right angles 
Mean Peripheral Eadius 
Adult 
Young 
-19 
0-8820 
0-9022 
-17 
1-1251 
1-1350 
-15 
1-3889 
1-4044 
-13 
1-6820 
1-6903 
-11 
1-9996 
2-0229 
- 9 
2-3463 
2-3630 
- 7 
2-7336 
2-7521 
- 5 
3-1529 
3-1666 
- 3 
3-6265 
3-6297 
- 1 
4-1397 
4-1254 
+ 0-9810 
4-7181 
4-6952 
