The North American monotomid fauna, north of Mexico, includes two described species of the genus Leptipsius Casey, 1916, L. striatus (LeConte, 1858) and L. dilutus Casey, 1916. Adults of L. striatus are redescribed and comments are provided on L. dilutus. A new species, L. imberbis, is described from specimens collected in New Mexico and Arizona. Based on a study of syntypes, the following species, previously included in the genus Bactridium, are transferred to the genus Leptipsius: L. brevicornis (Sharp, 1900), L. crassus (Sharp, 1900), and L. eumorphus (Sharp, 1900) [new combinations].