No. 453-] PYRAMIDULA ALTERNATA. 



663 



The number of specimens available for this study has not 

 been as large as is desirable in investigations of this kind ; but 

 as the three lots are of about the same number the results will 

 not be materially affected. 



In the tables of data the per cents, are indicated by a numer- 

 ator and the individuals or frequencies having the same per cent, 

 is noted as a denominator. 



IV. Discussion of Data. 

 The Rochester Shells. 



The shells from Rochester show a rather wide range of varia- 

 tion, as is seen in Fig. i, which is strongly trimodal. The most 



Table A. 



44 46 47 50 52 53 5_4 55 5_8 5_9 60 6][ 65_ 



T 5^ ^ y ^ T 4 8 3 12 I 2 I 



The number of shells examined was 67. 



