Another mystery Mammillaria... microcarpa perhaps

Can anyone help me out with a name for this plant? It looks like a microcarpa to me. But there are several other plants which all look very similar. I also have plants of M. thornberi ssp thornberi and M. sheldonii which are similar, but not the same.

As always, any suggestions would be much appreciated.

......... Si

I would suggest one of the mazatlanensis forms, can't really tell at the moment, it needs to grow more.

Hi Simon,
My first reaction was that this was M. sheldonii, but not microcarpa. My image of microcarpa is of more radial spines and finer spines that here, and maybe lighter central spines. M. sheldonii usually has heavier spines, and fewer radials.

But then I wondered if this could perhaps be M. mazatlanensis rather than M. sheldonii. They are similar, and equally variable, but normally mazatlanensis has slimmer stems and is more heavily branched. The flowers also tend to be of one uniform colour rather than shading from light to pale.

I do find it is quite difficult to be sure, as both species are quite variable, and maybe we need to wait until the plant is a bit older and one can see how it develops as far as offsets and branches are concerned.

Sorry I can't be more defintive - maybe others can shed more light.