Azuleja wrote:Gee, what about Mammillaria chionocephala or Mammillaria formosa? I think the flowers might be light pink.
From the picture the flowers look like they have yellow and red stripes, which combined with the over look of the plant gives it a pretty classic M. Karwinskiana ssp. nejapensis look. There are a lot of those out there, whereas M. chionocephala and formosa are less common to come across in my experience. The M. formosa flowers are generally much more white with pink stripes, whereas M. chionocephala tend to be much more white.
Of the remaining 3 Mamms in your pictures two (the third and fourth) are M. mystax and M. plumosa respectively, I think. The second one is really hard without flowers.
Here is a picture of M. formosa in flower this spring: