180 THE AMERICAN NATURALIST. [Vol. XXXVII. 



the breadth of the body -whorl. So the ratio of breadth to length, 

 or the voitricosityoi the shell, is a ratio of a slightly modified to 

 a much modified character. The actual length of the shell in 

 Fig. 4 is about 20 mm., its breadth, 17 mm., giving a ratio of 

 85%. But without erosion the length is estimated to have been 

 21.4 mm. giving a ratio of 79%. Thus the shell is now more 



ventricose by 6 degrees. In Fig. 3 the length is 15 mm., 

 breadth, 13 mm., ratio, 87% ; but the length without erosion 

 would be about 15.6 mm. and the ratio would be about 83 %, 

 an increase of ventricosity of 4 degrees. 



Thus within the limits of our studies we find that in all stages 

 of the growth of the shell of L. litorea there has been a change 



