Mammillaria have only one characteristic they don't share with any other genus: tufts or bristles or ? at the base of the tubercles. That is were the flowers form. If you see any little tufts, bristles... at the base of the tubercles, it is a Mammillaria.
Its now up to you Lindsey. Your photos are great but you are looking at the plant. A photo can't replace that. Are they both Mammillaria?
Daisy
