I rescently purchaced a shell in the bonnet/helmet group .It is interesting as
regards growth in that it seems to inticate growth not from th outer lip but
from the point where the last varix is.The next varix gets formed first and
then the shell behind it expands like sea floor spreading .Maybe Im just re
observing .This same shell has only one varix line for each body whorl.
 
regards
dave L.