From the states of Hidalgo Mexico, Mammillaria parkinsonii is one of the few Mammillarias that offset dichotomously, that is they literally split in two. Individual heads can be 6 inches tall and 3 inches around. It gets cream to pinkish white flowers.
     This one was allready splitting when I got it. Hopefully it will flower for me this season. The lower picture was taken at Bachs Cactus Nursery here in Tucson. I really don't know if it's one plant or three, but hopefully mine will look like that someday.