She's a beauty Darren, the purple flowers are always a real treat!
The genus name Notocactus comes from the Greek which means "southern cactus", the prefix Noto means south/southern... it may sound a bit wacky, but the name, as with botanical names in general, tells you something about the plant, so this genus of plants is found in the southern hemisphere ...in South America (Paraguay, Brazil, Uruguay).
The Genus Notocactus has now been transferred into Parodia, and this one is known as Parodia werneri... whilie I have tagged mine as such, I still prefer the old Notocactus epithet.
Enjoy your flowers, they hang around for a few days.
CP