Hardly a Niso specialist, but the genus is in the family Eulimidae,
along with Balcis, Eulima, etc.  There are quite a few species scattered
around the globe, on both sides of the Atlantic and both sides of the
Pacific.  Probably the most sought-after species is Niso splendidula
from West Central America.  It is one of the larger species and has
beautiful markings.  Most of the species are rather plain looking, often
completely white.
Paul M.