a full species in 1897 from specimens from Jalisco. In the same publication, he also described Oryzomys bulleri from nearby Nayarit, but he did not compare the two with each other. Merriam added a second species from Nayarit, Oryzomys rufus, in 1901, noting that it was smaller and more reddish than mexicanus. Goldman synonymized the three as O. couesi mexicanus in 1918 and in 2009 Carleton and Arroyo-Cabrales concurred, arguing that the differences between rufus and mexicanus were age-related and within the normal range of variation of the animal. Another subspecies, Oryzomys couesi lambi, was described by Burt in 1934 from central coastal Sonora, which extended the range of the species by at the time. This form is dark gray-brown, much darker than mexicanus, and has a shorter tail and weaker jugals. Carleton and Arroyo-Cabrales wrote that it is similar to mexicanus, but that further research is needed to determine whether it should be recognized as a subspecies. Large O. couesi from northern Sinaloa may also belong to this form. Goldman wrote that mexicanus was very similar to nominate couesi, but usually with paler fur; the upperparts are more buffy than in couesi and the underparts are usually white, but may be buffy, the normal color in couesi. Oryzomys zygomaticus was first described by Merriam in 1901 as a separate species similar to mexicanus, but with the zygomatic arches broadly spreading and curved downward. Goldman, who reduced it to a subspecies of couesi, recorded it from southwestern Guatemala and nearby Chiapas and described it as slightly paler than O. c. couesi but darker than O. c. mexicanus. Three specimens from central El Salvador have Cytb sequences similar to those of zygomaticus, but in The Mammals of El Salvador (1961), Burt and Stirton recorded only the subspecies couesi from the country, while noting that specimens from some localities were slightly paler than others. Interior Mexico Goldman grouped four subspecies of couesi from the interior plateaus of central Mexico together—albiventer, crinitus, aztecus, and regillus. Three of those (albiventer from Jalisco, crinitus from the Distrito Federal, and aztecus from Morelos) were described by Merriam in 1901, and Goldman had himself described regillus from Michoacán in 1915. According to Goldman, aztecus is pale and large-toothed, crinitus is large, dark and large-toothed, regillus is large and dark, and albiventer is large and relatively pale. In their 2009 review of western Mexican Oryzomys, Carleton and Arroyo-Cabrales