From the province of Minas Gerais in Brazil, Discocactus placentiformis is a flattened globular cactus to six inches around. That means this one is pretty much full grown and should be putting more of it's energy into it's cephalium. The cephalium is the wooly part at the top of the plant. It protects the young flower buds and fruit while they form. The plant blooms off and on throughout the summer and the flowers are white. Hopefully I'll be able to add a flower pic this season.

Closer view of developing cephalium

Closer view of spination