258 BUMPUS. [VOL. I. 



Genera/ Questions. 



The questions naturally arise: (i) Are the American shells, 

 together with their excessive variability, tending toward the 

 establishment of a new type? (2) Do they offer another 

 example of the principle of "mutation"? or, (3) Do the 

 variations arrange themselves symmetrically around the Old 

 World type? 



An examination of the several charts will show that : 



(a) While the British shells have an average stature of 89.6 



H -== 89.6 J, the average stature of the Amer- 



ican shells is 91, 



791.3 + 92.5 + 90.6 4- 92.2 + 90.0 + 89.7 + 89.2 + 90.8 + 91.1 + 92.6_ \ 

 \ 10 / 



The American shells are thus 1.4^ longer in proportion to their 

 breadth than the British. 



(b} While the British shells of 18 to 19 mm. in height have 

 an average weight of 1.85 grams, the American shells of the 

 same height have an average weight of 1.68 grams. The 

 American shells are thus .1 lighter than the British. 



(c} While the British shells of 18 to 19 mm. in height have an 



/2. 75-)- 2.50-}- 2.77 \ 



average displacement of 2.67 cc. ( - = 2.67 ] 



- see curve at right of Chart XIV - - the American shells of 

 the same height, even though they are lighter in average 

 weight, are relatively and actually larger, for their average dis- 

 placement is 2.80 cc. (Chart XIV). 



/2.75 + 2.71 + 3.05 + 2.62 + 3.05 + 2.55 + 2.62 + 3.05 + 2.82 \ 



- = 2.OO I 



\ 9 / 



"The shells from the Warren River, though extremely light, 

 having an average weight of only i .48 grams, are nevertheless 

 quite as bulky, that is, their displacement is quite as great as 

 that of the heaviest American shells of equal length. 



(</) While the color markings of the British shells are laid 

 down with precision, the color markings of the American shells 

 are indefinite and give a characteristic mottled appearance. 



