Mammillaria species- Flower Show, Mumbai
Cactus for ID : Flower Show,Mumbai : 230213 : AK-2: Another cactus seen at the Flower Show in Mumbai, during Feb, 2011.
A cultivated, potted plant.
That is a Mammillaria cv, monstrose something, can't remember the species 
Some kind of Mammillaria monstrose nudum, but I have no accurate id.