This name is a synonym of Mammillaria pennispinosa subsp. brachytrichion (Lüthy) U. Guzmán.
The record derives from Tropicos
(data supplied on 2012-04-18)
which reports it as a synonym (record 50335432) with original publication details: Kakteen und andere Sukkulenten 38(12): 295, f. 1987.
Full publication details for this name can be found in IPNI: http://ipni.org/urn:lsid:ipni.org:names:280329-2.
This name was in version 1 of The Plant List, record tro-50335432, and has not been changed.