Honv to Know Ajjierican Se ash ells 



IS 



The anterior end of the shell is that end which is in front when the ani- 

 mal is crawling. The aperture, the siphonal canal (when present), the head 

 and the tentacles of the mollusk are at this end. The posterior end is the 

 opposite, where the apex and nuclear whorls are located, hence it is some- 

 times referred to as the apical end. When we speak of the posterior side of 

 a rib or a bar of color we mean the side nearest to the apex or away from 

 the anterior end of the mollusk. The total distance between the two ends 

 of the shell is known as the length, although this measurement is often called 

 the height. 



■hlVICl.£(\(<. VlHORUS 



pftftveTAL. CALLUS 



COLUI*\eLl-f\ 

 SPlRftV- CORDS 



peRVPHtRY 



BODY WrtOftU 



LeNGTH 



OR 

 HEIGHT 



PftR»eTAL.V(ALL 

 BASE 



ANTERIOR OR 

 S\PHOMAL CANAL 



Figure 23. Parts of the gastropod shell. 



The aperture of the shell is the hole or space at the end of the body 

 whorl into which the mollusk can withdraw itself. The edge of the body 

 whorl which borders the aperture is known as the Up (sometimes called the 

 peristome in technical works). Sometimes the lip is thickened greatly or flar- 

 ing like an old-fashioned blunderbuss. Any startling development of the lip 

 is generally a sign of adulthood. If the lip thickens into an unusually large, 

 rounded, sharp rib it is known as a varix. Varices may be produced at various 



