NOTE ON A KACE OF CLAUSILIA ITALA 
(VON MARTENS). 
By W. F. R. WELDON. 
In the first number of Biometrika, I described the result of measuring one of 
the elements on which the character of the shell-spiral depends in a race of 
Clausilia laminata. A comparison between the variabilit}' of the "peripheral 
radius" of the shell, in young and in adult individuals, afforded strong evidence 
that this character was subject to a process of " periodic selection " in the race 
studied. 
In the early spring of 1902, I collected a number of individuals of G. itala 
(v. Martens) on the walls of the Citadel at Brescia, and I made a series of measure- 
ments of these, comparing 100 young and 100 adult individuals, as was done for 
G. laminata. The result of this comparison has been entirely negative ; there is 
no evidence of such a difference between young and adults, either in mean character 
or in variability, as to show that the elimination which occurs during growth is 
selective with regard to the characters measured. Although it is possible that an 
explanation of this result, not incompatible with the occui-rence of a selective 
process, may yet be found, I think it right to publish the result at once, because 
this is, so far as I know, the first case in which young individuals have been shown 
to resemble the adults of their race, in the degree of development of characters 
which may perhaps be called specific, so exactly that it is difficult to believe in the 
occurrence of any selective elimination during growth. 
The characters measured will be understood from the diagram, Fig. 1. Each 
shell was ground on a fine hone, until the columella was approximately cut in half 
along its whole length, the ground surfece having the shape indicated in the dia- 
gram. I^he length of the columella in an adult shell is roughly from 13 to 16 mm., 
excluding the bent portion connected with the clausilium, while its breadth is 
never half a millimetre. The plane of a section which passes sensibly through the 
middle of this long and narrow tube cannot make an important angle with the 
plane which contains the axis of the shell. In young individuals, where the 
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