I can't say for sure, but it seems to be Eriosyce curvispina var. robusta. Some cacti are quite variable, it's difficult to tell if there are tubercules but from the top view it looks like there could be. I can't see the pistil protruding from the middle of the stamens as seen on the following link, not sure if they are covered by the boss of stamens.
http://www.cactus-art.biz/sche...
The flower in the natural state looks a little different ..
https://www.google.co.uk/searc...
There's several varieties of Eriosyce curvispina ..
https://www.google.co.uk/searc...
