404 SHELLS AND SHELL-FISH. 



grown, forms another aperture. Sometimes, as in 

 Murex, these varices are irregular, and are either 

 spined or foliated ; but in the harp-shells they are 

 smooth and at equal distances. In Ranella they are 

 united, so as to form two lateral ridges ; while in 

 Triton they are detached and remote from each other. 

 In Cassis they are also alternate ; and, in the aberrant 

 species, none whatever are perceived. 



Volution. Synonymous with whorl. 



Whorl. Each complete turn of the spire in a spiral shell 

 is termed a whorl: the last, which terminates with the 

 aperture, is the body or basal whorl ; the rest are 

 the spiral whorls. 



