Please help me identify this Mammillaria

This picture was take at Huasteca Canyon, Santa Catarina, Monterrey, Nuevo Leon. I believe it is Mammillaria ritteriana and I have plants similar to it. But according to modern classification Mammillaria ritteriana is a synonym of M. chionocephala which is very different.
https://i.servimg.com/u/f22/13/02/58/84/ritter13.jpg

for me picture is too small to see any characteristics
i can`t see what is the number of central spines - for me is 1
Mammillaria discolor ?
http://www.koehres-kaktus.de/shop/images/Bildergallerie/koehres-kaktus-Bilder/Kakteen/Mammillaria%20discolor.Perote.-.01.jpg?XTCsid=7p2olmi5184u2em5p13qj6fb53
similar look for me on that picture

It certainly is from the right place to be M. ritteriana, and has longer spines that M. chionocephala.

But it doesn't appear to have formed much wool, or have any axillary bristles, both of which appear to be characteristics of chionocephala / ritteriana. I have both ritteriana and caerula, and they seem to be tighter spined plants than in your photo, with more wool / bristles, though not as much as the plant shown as ritteriana in Pilbeam.

From analysing the field data for NL and Huasteca Canyon on Mammillarias.net, the following have been identified from Huasteca Canyon, NL, though of course there could be more, the data almost certainly isn't 100% complete.

Mammillaria caerulea ?
Mammillaria heyderi
Mammillaria melanocentra
Mammillaria multiceps
Mammillaria plumosa
Mammillaria prolifera
Mammillaria ritteriana
Mammillaria spec.
Mammillaria winteriae

Now fairly clearly it isn't melanocentra, multiceps, plumosa, prolifera or winterae. So unless it is either new, or a species which isn't in the data looked at, then we are left with heyderi and ritteriana / caerula?

Without a bit more detail in the photo, or better still a flower, it could be difficult to say, as the plant in the photo doesn't fit my image of heyderi either. Sorry, Amante, that I can't be more specific. From my two trips so far, I have sene enough to know that you can't just rely on standard descriptions for recognition of plants in habitat, they vary so much.I guess if I had to choose, it would be ritteriana, and a form that perhaps because of location (shadier perhaps) hasn't got so much wool developed.

Thanks for all your help. I must apologize because the photo is not really that clear because at that time I took the picture there was too much haze. Coupled with the fact that one tries to hold on to dear life with one hand and take the picture with the other. All in all I took three pictures of the same plants and all came out a little diffused but hopefully with enough detail.

I have come to the same conclusion as you did, Chris, and for now I will stick to ritteriana. I have taken other pictures in that magical valley and all can be related to known taxa. Here are a few.
https://i.servimg.com/u/f22/13/02/58/84/dscf1416.jpg

https://i.servimg.com/u/f22/13/02/58/84/dscf1418.jpg

https://i.servimg.com/u/f22/13/02/58/84/dscf1419.jpg

https://i.servimg.com/u/f22/13/02/58/84/dscf1420.jpg