M. dubius Péringuey, 1901, nomen dubium
M. dubius was described from a single female from "Cape Colony". In the original description, Péringuey compared the new species with M. politulus and wrote that the two species were similar in shape, size and colour. The only difference between them was the shape of elytral intervals: those of the new species were flat and "the striate part sharply costate" whereas those in M. politulus were convex and sub-tectiform. Péringuey (1901: 302) however noted that "peculiar form of the intervals of the elytra may be cased by malformation" and the name given to the species suggests that the author was not sure about validity of this species.
The type of this species cannot be traced but Frolov & Scholtz (2005) examined a specimen with slightly concave elytral intervals, identified by Janssens as M. dubius and deposited in IRSNB, which is otherwise very similar to M. bias.
Péringuey, L. 1901. Descriptive Catalogue of the Coleoptera of South Africa. - Transactions of South African philosophical Society, 12, 1-920.
Frolov, A. V. & Scholtz, C. H. 2005. Revision of the southern African genus Macroderes Westwood (Coleoptera: Scarabaeidae: Scarabaeinae). Annales de la Société Entomologique de France (N. S.), 40(3-4): 371-391.