i 7 8 



THE AMERICAN NATURALIST. [Vol. XXXVII. 



shell, which is colored only in the inner layers. Comparison of 

 this section with hi-. 2 indicates that the two upper whorls of 

 this specimen contain openings 8,9, 10, and n, as shown in 

 Fig. 6. The uppermost whorl has almost disappeared and the 

 second one has lost the entire outer wall of both primary and 

 secondary shell. So that of the shell formed during the stage 

 of Fig. 2 there remains in this specimen only the columella of 

 the two lower whorls and a portion ot the lip region. While of the 

 stage of Fig. 1 there remains only the merest fragment of the 

 body-whorl (Fig. 5). 



The actual shortening of the shell and the changes in shape 



them by comparing sections of younger and older stages, as in 

 Figs. 5 and 6. By this method it is estimated that between 

 the stages of Figs. 1 and 2 there has been a shortening of about 



4 to 1.4 mm. Or considering Fig. 1 as the initial stage of all 

 the larger shells, the length of that portion of the shell has been 

 reduced in the three subsequent stages by 8.3%, 20.0%, and 



