I was off-line for a few days with monitor trouble (a helpless feeling:
a couple of months after acquiring  one of these
calculators-on-adrenaline, i suddenly find myself  (especially
businesswise!) dead-in-the-water without it!!), and could not believe my
eyes when dozens of messages about one of my favorite spp- the humble
"Americain dogwinkle" tumbled out.  It is surprisingly variable on both
sides of the Atlantic, and adjacent populations  can be more different
from each other (with respect to color and pattern, ie- in form,
populations  vary much less than comparable Nucella lamellosa
populations on the west coast)  than one would normally anticipate ( i
think it develops directly, with no larval stage, so each population is
more-or-less genetically isolated) .  I have seen and sampled this
adaptable species at numerous localities, so would like to make a few
comments about some of the issues raised by you wonderful conchlers:
        1)  Nova Scotia is not the edge of the known universe, and most
certainly not the northern extreme of N. lapp.'s range: it gets half-way
up Labrador!  As for spp displaying  an increased range of variability
at the edges of their range, i was of the opinion that it was usually
the other way around.  For example, Placopecten magellanicus Gmelin, our
well-managed commercial scallop, is not nearly as varied near Cape
Hatteras, or off Newfoundland, as it is around the Bay of Fundy (its
most heavily populated region), and the N. lappilus in Labrador are
positively anemic- shades of off-white and brown, mostly.  Another good
example is Neptunea despecta, which is riotously variable in form in its
prime range, Newfoundland waters, with more named formae than one
normally wants to think about!  However, way down here in New Scotland,
it is absolutely boring, and  quite uncommon.  A species which becomes
more variable at the extreme edge of its geographic range, must be
unusual, to say the least!
        2) The maximum variability for N. lapp.,  occurs on exposed  habitats,
where the waves and winter ice keep algal cover to a minimum, and the
poor dogwinkles are exposed most of thier lives, in plain view of any
and all predators.  Where seaweed covers the population completely, as
at Victoria Beach (best chiton-collecting locality in the entire
province!!) (across from Digby), nothing but whites, grays, and muted
browns can be found.  Visual predation patterns would seem to be a
factor here, and perhaps the large range of colors (and to a lesser
extent, patterns) is produced by several predators, each of which finds
different morphs easier or harder to distinguish.  Or, perhaps the
predators' search techniques change in response to varying  frequency
shifts (for example, perhaps seagulls selectively start looking for the
brown ones, after they have eaten most of the orange specimes in a
particular area, giving the orange allele a chance to recover, instead
of being wiped out), thus encouraging a high degree of variability,
since no morph is likely to be extripated.