The recording in 1992 of an unknown antbird loudsong initiated a journey of discovery that led to the resolution of the conflict between John Zimmer (1932) and Melvin Carriker (1934) regarding the taxonomic standing of the population of Myrmeciza hemimelaena, a widespread southern Amazonian antbird, that occurs in lower Andean elevations in San Martín, Peru. Zimmer had described a new subspecies, M. h. castanea, from the Moyobamba Valley, but Carriker, on the basis of specimens he collected at the same elevation in an adjoining valley, could not find morphological differences between his specimens and the widespread nominate form of M. hemimelaena. Both authors were correct. Two cryptic sister taxa coexist in the foothills of San Martín. Diagnostic vocal and morphological characters and syntopy confirm their status as distinct species. Myrmeciza hemimelaena castanea Zimmer is revived and raised to species status. Concurrently, analysis of the vocalizations and morphology of the lowland population north of the Río Marañón in Peru, the loudsong recording of which initiated the project, revealed that this population was closely related to M. castanea of which it is described as a subspecies, M. c. centunculorum, under the biological species concept. The discovery that there are two cryptic species in the Myrmeciza hemimelaena complex exemplifies the continuing need to pursue field knowledge and analysis of avian species limits in the Neotropics required for the development of conservation strategies as well as phylogenetic understanding.