14 ITS MARKINGS. 



Sometimes the animal pauses for a considerable 

 time before it builds another whorl to its shell, and 

 during this time it spends its strength in thickening 

 the outer lip, or throwing out a ridge or frill ; after 

 this it goes on smoothly for awhile, and then builds 

 another ridge. Each of these periodical elevations, 

 which thus vary the surface of the whorl, is called a 

 varix. 



The number of varices to a whorl differs as much 

 as their shape ; some shells having but two, others 

 three, while still others have many of these distinctive 

 markings. 



The varices on this shell are best seen in young 

 specimens, and consist of nine rounded ridges to a 

 whorl. In full-grown specimens the body whorl has 

 no distinct varices, and those on the spire become 

 somewhat worn off and obliterated. Quite often a 

 piece of the outer lip gets broken off by an accident ; 

 then the patient animal builds on a new lip, often 

 leavinof a bigf scar to show where the break was re- 

 paired. 



Inside, the shell is of a dark-liver color, with lighter 

 spiral lines ; without, it is about the same color, but 

 is generally covered with an ash-colored powder, 

 giving it a dingy appearance. 



Now that we have examined the parts of the shell, 

 let us study the living animal, which all this time 

 has kept itself concealed in this spiral tube. 



We will put a few of our specimens into a glass jar 

 of sea-water, and watch their motions. 



First, from out the aperture comes a little brown 

 scale, which serves as a door, and which the tenant 

 had closed after he had withdrawn himself into his 

 house. This door is called the operciilmn. We shall 



