5 1 8 THE AMERICAN NA TURAUST. [Vol. XXXV 1 1 . 



this change of plane of coiling the second whorl partly buries 

 the earliest portion of the first whorl or protoconch. 



For about half a volution or less, the shell is smooth, although 

 lines of growth become more pronounced. At more or less regular 

 intervals stronger lines of growth appear (ananepionic). In the 

 later portion of the nepionic stage (metanepionic) longitudinal 

 wrinkles or ribs appear which characterize the ambital portion of 



two whorls. At about the same time or, in' some cases, appar- 

 ently earlier, faint revolving lines become visible on the shell. 



They are nearly uniform, those on the ambitus being slightly 

 stronger. They represent the earliest part of the primary spirals 

 so pronounced in later stages. Almost immediately after the 

 inception of the vertical wrinkles or ribs, an angulation appears a 

 little above the ambitus of the whorl, which thus becomes divided 

 into shoulder and body portion. At the same time the ribs 



