I have a bunch of Mammillaria books, most are very old and the nomenclature of these plants has changed (and is still changing) so much that it is hard to use any of them because you can often get multiple names for the same plant depending on which book you use.
A fairly recent one is the book 'Mammillaria' by Pilbeam, in it the entry for M. melanocentra sup melanocentra states that there are 7-9 radial spines of unequal length, with the lowest longest, they start black but with age turn pale grey with black tips. The central spine is much longer and stronger also black usually pointing somewhat upwards. Flowers are pink-carmine and will appear from between the tubercles - flowering is usually preceded by appearance of wool in between the tubercles.
I think that matches up pretty good. I am pretty sure I have two of these. I have had a hard time keeping them decent looking - these plants want plenty of root space, once I added them to larger multi plant bowl shaped pots they started doing better. I have no good pictures of them - something I will try to remedy.
