2S6 MANUAL OF ZOOLOGY sect. 



on the axis. When the obliquity is very slight (Fig. 174), 

 the spiral is nearly flat; when the obliquity is great, an 

 elongated tapering shell, such as that represented in Fig. 

 175, is the result. Sometimes the later whorls completely 



Fig. 172. — Shell of Triton nodiferus. Natural size. New Zealand. 



cover over the earlier ones, so that the spiral form of the shell 

 is concealed. Sometimes only the apical portion of the shell 

 is spiral, the remainder being a straight or sinuous cylinder. 

 The mouth of the shell has usually a prominent margin or 



