No. 435 ] SHELL OF UTTORINA LI TORE A. 179 



46.7% respectively. This amounts to a reduction in the total 

 length of the shell at each stage of 5%; 4% and 7% respec- 



Assuming that, if there were no erosion, the outline of the 

 section at the stage of Fig. 4 would be represented approximately 

 by the combined continuous and dotted outlines in Fig. 5, it is 



