Micronycteris sensu stricto is a diverse group of small to medium-sized phyllostomid bats characterized by large rounded pinnae that are connected at the base by an interauricular band of skin. Eight species are currently recognized, including three with dark venters (hirsuta, megalotis, microtis) and five with pale venters (brosseti, sanborni, schmidtorum, minuta, homezi). As many as seven species can occur sympatrically at Amazonian localities. In this paper we describe a new dark-bellied species from the lowlands of northeastern Peru and document its diagnostic external and craniodental characters. We also summarize information about diurnal roosting habitats for the new species and its Amazonian congeners, and we emphasize the importance of nonconventional collecting methods for future studies of phyllostomine diversity in Neotropical rainforests.