446 PROCEEDINGS OF THE ACADEMY OF [June, 



(6) White lip of the apperture is quite common in some localities. 

 In fact, purple is rarely found not associated with a trace of lighter 

 color on the lip. This white lip may be combined with all colors 

 and dilutions. 



(7) Narrow stripes. In many shells about ten narrow white stripes 

 are found on any color background. 'These are sometimes associated 

 with the ridges which appear on many shells. 



(8) Wide stripes of white, usually two in number, often appear. 

 The widest stripe equals two or three of the narrow ones and the 

 smaller stripe is double the width of the narrow ones. The widest 

 stripe is always posterior to the narrower stripe. 



(9) Spot of purple on the columella. This is rare at Mount Desert, 

 but very common at Rye Beach, New Hampshire. 



(10) Imbricata. A fluting of the ridges of the shell gives rise to 

 the variety called by Lamarck imbricata. 



Apparently each one of the ten characters recognized may be 

 combined with any other. If this is so there must be 1,103 varieties. 

 Not that many varieties have been found. This is due to the fact 

 that one cannot distinguish certain combinations from one another. 

 As an example, let us consider the case of the colors alone. We have 

 purple, chestnut, yellow, and white. There are eight possible combi- 

 nations of these: white, purple, chestnut, yellow, purple-chestnut, 

 purple-yellow, chestnut-yellow and purple-chestnut-yellow. These 

 last four are shades of olive and chocolate, and cannot be distinguished 

 easily from one another. If we combine these four color combina- 

 tions into one group and omit the white lip and purple spot on the 

 columella, we will reduce the possible number of variations to be 

 recognized from 1,103 to 33. Twenty-eight of these thirty-three 

 varieties have been recognized. However, there are five that are 

 so rare that they were not discovered in a collection of six thousand 

 shells when they were particularly sought after. These were narrow 

 stripe dilute yellow, wide stripe narrow stripe yellow, wide stripe 

 narrow stripe dilute yellow, narrow stripe dilute olive, and wide 

 stripe dilute olive. The yellows which contribute to the olive color 

 and the dilute are much rarer than any of the others, so it is no 

 wonder that they are the ones that would be lacking in combinations. 



It is obviously impossible to attempt to correlate all the known 

 varieties with environmental factors, so the writer has for the sake 

 of convenience reduced still further the number of groups. The 

 particular groups recognized are as follows: 



(1) White; that is, pure white. 



