Potentially a Pediocactus simpsonii...http://plants.usda.gov/java/profile?symbol=PESI

Good luck!

Some kind of Mammillaria. Pediocactus have stouter curved centrals.

If it has nice clear yellow blooms it's Mam. baumii. here is a pic of mine.

Is there another plant in the same pot? If so, do you know what is it, maybe post a close-up? I circled it in red in your photo.
Thnx. Rina

That circled plant looks like Lenophyllum texanum, Rina.

yes, there is another plant in it, i actually separated and repotted it, i will take a pic soon.

ill take a apic of it soon, i actually repotted it separately

ill take a apic of it soon, i actually repotted it separately