Also from Tamaulipas, Mexico, Mammillaria carmenae is a clumping globular cacti with stems to two inches around and three inches high. The soft fine spines are gold. It requires regular watering in summertime but should be planted in a quick draining mix as it's prone to rot. Small cream colored or white flowers appear in late winter.
     This is one of the few pettable cacti, the spines are soft and flexible. I had several of these but lost them to rot. This one clump is the last to survive in the ground and seems to be doing OK. The offsets are easy to root and luckily I got to them before the rot did with the others.