No. 453-] 



PYRAMIDULA ALTERNATA. 



665 



The Bowmanville shells are the most variable of the three 

 lots, the curve showing a marked multimodal tendency, which 



always stands for extreme variability. The range of var 

 is from 46 to 87 per cent. There are four modes of i 

 nence, at 50-53, 57, 59 and 65, with frequencies of 5, 10. 

 5, respectively. It will be noted that the curve for the 

 manville shells is very similar to that of the curve for the 

 ester shells, the peculiar broad mode being present in 

 The data for this curve is shown in Table C. 



Table C. 



4^ 53 54 51 56 57 5^8 59 ^" 



I 5 5 I I 2 10 6 9 

 65 67 68 70 72 72 75 ZZ ^' ^~ 



5" 7 T y T 2 2 I 2 2 I > 



The number of specimens examined was 85. 



V. Comparison of the Thkef. Locai.i 1 ik.>. 

 Figure 4- 



In comparing the three localities 

 Bowmanville and Rochester shells r 



