Here are my two cents worth:
In Boston Harbor (George's Island, to be more particular), Nucella lapillus
is brown, orange, or white, no striped (bizonalis) forms at all.  The
aperture is frequently bluish/purple or rather bright yellow, sometimes
white (always on white specimen).  The sculpture is interesting in that the
majority of specimen have more or less raised cords, though many are also
smooth.  Among those with raised cords, some show the beginning of the
'raised lamellae' form that Constantine described, although you have to go
to at least a hand lens in order to visually make out the few lamellae that
are actually there.  The texture is quite rough, though, you can feel which
specimens have these few lamellae, even if you can't see them.
It's lots of fun to collect them there, although Boston Harbor is still
polluted (true progress is being made, however) and many specimen show an
oily blackish dorsum that detracts from the otherwise considerable
attractiveness of these specimen.
 
Monika