The grass-feeding genus Gracilimiris Stonedahl and Henry, 1991 is reviewed and G. rubrolineatus new species, from Arizona and Texas, USA, is described. Provided are a diagnosis, description, and digital images of the adult male and female and male genitalia of G. rubrolineatus; diagnoses, male habitus images, and summary of hosts and distributions of the three previously described species; and a revised key to species to facilitate identification.