Mammillaria erythra
Reported from Veracruz, on the border with Puebla, at Puerto del Aire, 1850m altitude on limestone conglomerate, this species seems to be merely a short spined form of the variably spined M.mystax from this general area.
Hunt has recently maintained it as provisionally accepted, althought previously he was more positive in his ascertion that it "is simply a distinctive form with reduced spination".
I favour his earlier opinion
Mammillaria - John Pilbeam pag.325
Mammillaria erythra
From "Ento" Ennio Toso collection - Savona
Referred to Mammillaria mystax