Unknown Mammillaria 2 -> Mammillaria hahniana

I took the picture in a cacti exhibition in Madrid. No idea about the species of this Mammillaria.

Regards,

Hi,
I would suggest m. formosa.

After watching dozens of pictures, I think you're right. A very variable species indeed. Thank you.

I would not exclude the possibility that it is M. hahniana (or possibly the related M. albata). In general, M. formosa (or chionocephala) has somewhat more brownish spines than the plant of the photo. And I have not yet seen a dichotomously dividing formosa, although I will not exclude that it might be possible.
Also, the presence of hairs seems to point towards M. hahniana.
If you look at M. hahniana on Maurillio's pages of the website, then you will see M. hahniana WTH845, which looks very much like your plant. I even found a dichotomous WTH 845, also shown on that page.
What is the flower colour? If it is reddish, then that would be a atrong indication for hahniana.

Wolter ten Hoeve.

I'm afraid isn't a plant of mine. I saw in a cacti exhibition. So it's very improbable I see it again. In any case, based on your reasoning, I think the option of M. hahniana is more correct than that of M. formosa. I'll tag it that way. Thank you very much.