Sorry I didn't introduced myself earlier. I have already asked for some IDs.
I have a collection of xeric plants, not specialized in Mammillaria at all, but I really like this genus.
For some reason, when I started collecting cacti, I decided to avoid Mammillarias. I used to think about then as uninteresting plants, found in supermarket side by side with African violets.
But after purchasing some and giving them the correct conditions, I have learned that they can be amazing (it was a M. nejapensis that showede that).
Now the Mammillarias are among my preferred plants.
You guys can see some pictures of my collection in Instagran (marcelo_cactos_etc).
Thanks for the opportunity in taking part of this community.