666 THE AMERICAN NATURALIST. [Vol. XXXVIIl. 



closely in the form of their curves, which is quite different from 



Bowman ville 57 '/.^ 



Rochester 59 

 Auburn 57'/,. 



The mean per cent, for the three localities is as follows : 



Bowman ville 65.1 

 Auburn 59.7^. 

 Rochester 54.1^0. 



This shows that the Bowmanville shells have relatively the 

 highest spires, while the Rochester shells have the lowest spires. 

 1 he widest x^riation is found in the Bowmanville shells, where 

 the extremes are 46 and 87 per cent. 



per'crt"shTwfth??.L'^^' ?! ^"^ ^"^g^* ^^^^^ the same; hence the 



relation of height to diameter. 



