The Mammillaria melanocentra that is native to northern Mexico. It has a short blue/green cylindrical body and has large pyramid tubercles and wooly axils. From the tip of each tubercles is an areole which produces one central spine and six to nine radical spines that are black but fade to grey leaving only the tips black. This cacti can grow up to 16cm high and 15cm in diameter. It can produce pink flowers in summer in a crown on the top of the plant. 

RATING- Easy

LOVES- Well draining, porous soil. Lots of bright light.

HATES- Water-logged soil.

Pot diameter 10.5cm

More information and care recommendations are below.