ID Mammillaria asked

I received this picture from W. Lehmann. He bought this plant with the name: Mamm. leptocaulis.
I did a long search on the internet but found nothing under this name.
I think this plant could be M. johnstonii, more like the form sancarlensis, but off course I could be wrong;
What do you think?

I think that is certainly a possibility, Hugo. The curved upper central is quite distinctive, although some older areoles appear only to have 1 central. Maybe the lower central appears later on as the plant matures a bit. It would be interesting to know the flowers.

Its an odd name though, as lepto means thin or slender, and caulis means body. so this is a thin or slender bodies Mammillaria. M. johnstonii is certainly not that, usually a smallish but usually subspherical plant. So where that name came from, I don't know.