(This plant comes in a 3.5 inch 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. The plant is shipped in its pot to prevent any damage to the roots).
This is one of the Mammillaria commonly called "Owl Eye Cactus", known for dichotomous branching (forking or dividing into two parts).
Cultivation: This plant is easy to cultivate but very slow growing. Cultivate it in a well drained and mineral substratum. Water regularly. It need full sun, so it keep a compact and flat shape. It does not tolerate intense cold, but tolerates some cold if kept dry. Frequent transplantations of the young plants protect the lower part of the stem.
Some of the information in this description has been found at desert-tropicals.com, llifle.com and cactus-art.biz