Hi Nancy,
You may know that Strombus alatus was once considered a subspecies of S.
pugilis, but now they are considered separate species. However, S.
alatus is the common species in Florida (type locality is Sanibel
Island, Lee County, FL), while S. pugilis is the common Caribbean
species, (type locality is Montego Bay, Jamaica,). So collecting
locality becomes very important in dietinguishing one from the other. If
it is from the islands, it is not S. alatus. If it is from Florida, it
is most likely S. alatus.

While Walls mentions that the penultimate spines in S. pugilis are
larger/longer than those on the ultimate whorl, there are pictures of S.
pugilis in Renato Moscatelli's little "The Superfamily Strombacea from
Western Atlantic" (1987) which show several specimens from Brazil with
shorter spines in the penultimate whorl than the ultimate whorl...just
like S. alatus.

As Tom E. says, the most common way of distinguishing the two species is
examining the posterior end of the outer lip. In S. pugilis, it hooks a
bit upwards (spirewards) and rolls in a little bit more toward the body
whorl while in S. alatus, it angles downward and tends to flare outward
a bit more, away from the body whorl. But exceptions and local
populations may abound. Though with a floating veliger stage as a part
of their developmental history, local populations may not be near so
homogeneous as in Melongena corona and their kin.

The colors are also mentioned: for S. pugilis, the body whorl is usually
a clear orange to red-orange or what is called salmon color, with a
reddish or orange glaze commonly on the aperture (this may be violet in
some specimens, and white in albinos, of course).

For S. alatus, colors are generally darker. The glaze on the apertural
area is often dark brown to blackish, though it may also be orange or a
lovely deep violet (or again, white or perhaps pinkish, in albinos)

But what Walls does not mention is the color pattern of S. alatus. He
does not mention the very frequent banding of the shell and lets the
color pattern it usually exhibits go with a sparse "mottled."  S. alatus
is often patterned and usually banded in white.  The pattern can be
tented (triangles) or maculated (irregular to squarish). This S. alatus
pattern is especially apparent in juveniles.  A faint band is usually
apparent even in the darkest adults. I do, however,  have a specimen of
S. alatus from Sanibel many years ago that has no trace of a band.

I have seldom seen a trace of pattern in S. pugilis...though my
experience is less with s. pugilis, and I note that Moscatelli
illustrates a great number of juvenile S. pugilis, and none shows a
pattern, though a few adults and juveniles show faint banding.  The
pattern may be a good way of distinguishing juveniles. Of course the odd
specimen may occur that belies this distinguishing feature, it is likely
to be true almost always.

Variability and color in S. alatus:  We were on Carl Johnson State (?)
Park once, many years ago...the beach was covered with live s. alatus,
and every wave was bringing more ashore. We at first tried wading way
out as far as we could with buckets of them, gently restoring them to
water that was less wave-tossed. But we did not know their habitat there
and they seemed to keep coming...a job too big for us. So we began to
look for oddities. Especially sinistral shells, which we did not find,
and albinos which are relatively common on Marco Island, but apparently
not on Carl Johnson which is north of Marco. But we did find that, there
on Carl Johnson, most specimens were brown, banded in white, with a dark
red-orange-to brown glaze. Some, even very mature ones, were strongly
maculated on the dorsum. An occasional shell would have a nearly black
apertural glaze and a dark brown dorsum, faintly banded. And a very vew
has a clear deep violet apertural glaze on a light brown shell. It was
an interesting experience in the local variation of a species. We
collected one of each color form. They have faded over the years and
don't live up to my memory.
Lynn Scheu,
Louisville, KY