Key foundational elements of taxonomic description were omitted in the original naming of species-group taxa now recognized in the Malagasy genus Nesomys: N. rufus Peters, 1870, N. audeberti (Jentink, 1879), and N. lambertoni G. Grandidier, 1928. Based on our review of the material available to the authors, we identified the holotype by monotypy of N. rufus, designated lectotypes of N. audeberti and N. lambertoni, restricted the type localities of N. audeberti and N. lambertoni, and localized the probable geographic source of the holotype of N. rufus. Refinement of the geographic source of N. lambertoni and N. rufus illuminates the incorrect placement of their type localities as currently interpreted and brings them within the presently understood distributions of those species. Extensive discussion is devoted to the travels of J. Audebert and A. Crossley, collectors not only of the types of N. audeberti and N. rufus, respectively, but also of important series of lemurs that remain relevant to understanding the taxonomy and distribution of these endangered mammals.