On Long Island, my old stomping grounds, the southern-most extent of its
range in North America, Nucella lapillus is rather uncommon.  It is limited
to the eastern reaches of the island along the south shore.   The imbricate
shells which were given the form name imbricata Lamarck, 1822 are almost
non-existent on Long Island, whether found in the calmer inlets, or exposed
rocky shoreline.   There might be a correlation between shell sculpture and
water condition in other areas, but not for Nucella lapillus on Long
Island.  The Long Island shells are also rather drab and unicolor.  So some
of the ecological notes and theories proffered over the past couple of days
do not fit into a nice neat package on Long Island.  Maybe some on the Long
Island Shell Club members on the list can add, or update some of my field
notes.
 
Rich Goldberg