A new genus name Notaferrum n. gen. is proposed for Ptinus natalensisPic, 1906. The taxon is diagnosed and described and the only known species redescribed. This taxon, well outside the concept of the genus Ptinus Linnaeus, 1766, is most distinctly characterized by a pair of longitudinal and vertically oriented blade-like ridges located medially on the pronotum, a previously unknown feature in the spider beetles and the more inclusive Bostrichoidea Latreille, 1802. This species is a probable symphile of the African species of weaver ant (Oecophylla longinoda Latreille, 1802), based on both a collection record from inside an ant nest as well as the presence of distinct trichomes on the pronotum. This taxon represents the first record of a spider beetle associated with weaver ants.