Hello, CONCH-Lers!
I think I know why my confusion. Instead of having mixed
up the localities, I apparently have nigritis and
ambiguus,
not nigritis and radix. I failed to consider ambiguus as
a possibility for the one species.
hanks,
Linda
P.S. Now all I have to get is a specimen of Radix, so
that I have the three species to examine (assuming that
ambiguus has specific status).