Hola Victoriano,

As you surely know, Cypraeidae Systematics is quite a mess. I decided to
follow Lorenz here because, tough not satisfying everyone, his work is very
complete and coherent.

He groups under Staphylea genus two kinds of species, one unnominated group
consisting of inflated shells (S. limacina, S. semiplota and S. staphylea)
and other group known as "nucleolaria group", with S. nucleus and S.
granulata.

However, this groups seems not to have a real taxonomic value, so the
correct name must be Staphylea nucleus. There are two subspecies of it: S.
nucleus nucleus living in a great Indopacific area centered in Philippines
and S. nucleus madagascariensis living in East Africa.

I hope this will be useful, I´m sorry I couldn't help more on Mitrella
semiconvexa issue.

And, by the way, Feliz Navidad to everybody out there,

Best wishes,

Alfonso Pina
Málaga, Spain
www.eumed.net/malakos