due to the rapid growth and approaching maturity of the 

 young ones. That the ratio of the two dimensions used 

 changes somewhat with age is shown in a later table 

 (Table VII), a fact that somewhat complicates a compar- 

 ison between shells of any two localities. It will fur- 

 thermore be observed that the variability of the Vine- 

 yard Sound shells as indicated by their standard devia- 



its maximum upon the latter date, but that for both the 

 Buzzard's Bay localities the same is not true; on the con- 

 trary, in the case of Penzance Point the August 5 collec- 

 tions showed the least variability of any time. The fact 

 that the maximum of the shifting seasonal variation does 

 not occur at the same time in localities almost within 

 sight of each other, as in the present instance, plainly 

 indicates that comparisons of variabilities based upon 

 the time-factor alone do not take everything into consid- 

 eration. The shells from Buzzard's Bay range in their 

 arithmetical mean from 58.030 to 60.308 while those from 

 Vineyard Sound, separated from the former only by the 

 narrow tongue of land on which the village of Woods 

 Hole is located, form a distinct class ranging from 60.978 

 to 64.022. Here is a distinct place difference in the shells 

 of the two general localities in question. 



Shells obtained from other localities in Buzzard's Bay 



