Abstract: Passalus (Mitrorhinus) nodifer sp. nov., from the extreme west of the Brazilian Amazon in the state of Acre is described and illustrated. The new species can be recognized by the head with conspicuous and strong single secondary tubercle; frontal ridges straight and well-marked; mandibles with two apical teeth; aedeagus with parameres reduced with large and rounded apical margin and basal piece with a deep V-shaped notched in the medial region.

Resumen: Passalus (Mitrorhinus) nodifer sp. nov., del extremo occidental de la Amazonía brasileña en el estado de Acre se describe e ilustra. La nueva especie puede ser reconocida por la cabeza con el único tubérculo secundario conspicuo y fuerte; quillas frontales rectas y bien marcadas; mandíbulas con dos dientes apicales; edeago con parameros reducidos con margen apical grande y redondeada y pieza basal con una muesca profunda en forma de V en la región medial.

Foram efetuadas coletas mensais de julho/1990 a junho/1991, durante a lua nova, na Fazenda Aruanã, uma área de terra-firme às margens da rodovia Torquato Tapajós, AM-010, Km 215, Município de Itacoatiara, Estado do Amazonas, Brasil. Utilizou-se para as coletas luz mista de mercúrio de 250 W, sobre um lençol branco. Foram coletados 251 indivíduos de 9 gêneros e 18 espécies de dinastíneos e dentre estes houve predominância de Cyclocephala Latreille (3 espécies abundantes) e Ligyrus Burmeister (única espécie abundante).

Monthly collections were done between July/1990 and June/1991 during the new moon at the Fazenda Aruanã an area of upland rainforest located alongside the Torquato Tapajós road, AM-010, at Km 215, city of Itacoatiara, Amazonas State, Brazil. A mixed 250 W mercury vapor lamp was used for atraction on a white sheet. 251 specimens of 9 genera and 18 species of Dynastinae were collected and there was predominance of Cyclocephala (three species were more numerous) and Ligyrus (only one abundant).