Mammillaria calleana - Backeberg
Needless to say there was no original type deposited and the location was given merely as Mexico, Hidalgo. This has rendered this species as dubious for some time. Mottram did propose Backeberg's illustration as lectotype. Reppenhagen claims to have found the species atMetztitlan, Hidalgo, Repp.1917 and he claims it is quite rare. I have no experience of this plant and can only say that Reppenhagen's photograph shows a plant very similar to M.wildii. Undoubtedly the plant also corresponds to the rather brief description given by Backeberg.
From " The Journal of the Mammillaria Society" vol.37 n.3 - August 1997
Metzitlan - Hidalgo - Mexico