Mammillaria shiedeana 

(This plant comes in a 3.5" pot. You will receive a very similar plant to the one in the picture. It may or may not be blooming at the time of your purchase. This plant is shipped in its pot to prevent any damage to the roots).

Cultivation: It is a slow growing species of easy culture, recommended for any collection, it doesn't require any special treatment. Water regularly in summer, but do not overwater (Rot prone) Use pot with good drainage and a very porous potting media, keep dry in winter. It is quite frost resistant if kept dry, hardy as low as -5

Sun exposure: High levels of light are needed to flower and for good spine development. If grown correctly, it will reward the grower with generous displays of purple flowers. Clustering in cultivation after several years and easily flowered. For best results, use a shallow pot, and only use the smallest diameter pot that will accommodate the plant. 

Origin:  Mexico (Tamaulipas)

Habitat: Grows among rocks, on fertile soils rich in dark organic material produced by the decomposition of vegetable matter in open pinion woodland, 700-1400 mt altitude.

Propagation: Direct sow after last frost (usually) or division, wait until the offsets that appear at the base of old clustered specimens are 1/3 the size of the parent and then detach and plant. (Cuttings root quickly)
 

Some of the information in this description has been found at desert-tropicals.com,  llifle.com and cactus-art.biz