Not mammillaria, don't know what it is. Mamm, are comprised of a composite of "tits", thus the name.
Looks like Hamatocactus setispinus.
Funny. Swore I posted here yesterday. Oh well.
I recently got a Hamatocactus Hamatocanthus. The spines and rub shape remind me of it but the ribs aren't as defined as mine. Mine come almost to points. But the glochid structure is identical.
Huh... Stush has the hiccups. :P
Too funny Planto ! LOL!!