Hello!
Hi Favio,
There are two species;
Umbilia armeniaca (Verco, 1912)
Umbilia hesitata (Iredale, 1916)
The rest are only color forms or geographical variants.
IF you can obtain series of shells (quite expensive for
the overpriced armeniaca) you will probably find intergrades
among all of the forms/species.
Later,
Emilio Jorge Power