S17 e 
r 
umbilicus 

Figure 8. - Shell terminology. Shell with whorls increasing gradually 
in size, (a); whorls rapidly increasing in size, (b); sunken spire, (c); 
straight outer lip, (d); curved outer lip, (e); lip retracted to the 
suture, (f); method of counting whorls, (g); straight (not reflected) 
lip, (h); reflected lip, (i); sutures slightly indented, (j); sutures 
strongly indented, (k); crenulate sutures, (l); truncate columella, (m); 
straight columella, (n); carinate periphery, (0); angular periphery, (p); 
round periphery, (q); round aperture, (r); oval aperture, (s); narrowly 
oval aperture, (t); roundly lunate aperture, (u); ovate-lunate aperture, 
(v); narrowly ovate-lunate aperture, (w); broadly lunate aperture, xs 
deeply lunate aperture, (y); umbilicate shell, (z); perforate shell, (aa); 
imperforate shell, (ab); multispiral operculum, (ac); paucispiral 
operculum, (ad); concentric operculum, (ae); concentric operculum 
with spiral nucleus,/(af). 
