more narrowly distributed species with peripheral distributions together form the O. couesi group within the genus Oryzomys. The eighth species of the genus, the marsh rice rat (O. palustris) is the only member of its own group (unless western populations are classified as a separate species, O. texensis). Oryzomys previously included many other species, which were reclassified in various studies culminating in contributions by Marcelo Weksler and coworkers in 2006 that removed more than forty species from the genus. All are placed in the tribe Oryzomyini ("rice rats"), a diverse assemblage of over a hundred species, and on higher taxonomic levels in the subfamily Sigmodontinae of the family Cricetidae, along with hundreds of other species of mainly small rodents. History Edward Alston first described Oryzomys couesi in 1877, using three specimens from Mexico and Guatemala. He named the animal Hesperomys couesi, placing it in the now-defunct genus Hesperomys, and noted similarities to the marsh rice rat (then called Hesperomys palustris) and two species now placed in Tylomys. The specific name, couesi, honors American naturalist Elliott Coues, who had done much work on North American rodents. In 1893, Oldfield Thomas wrote that the species, by then placed in the genus Oryzomys as Oryzomys couesi, had caused much confusion about its identity, because the three specimens (one from Cobán, Guatemala, and two from Mexico) used by Alston in fact belonged to two or three different species. He restricted the name couesi to the animal from Guatemala, and introduced the new name Oryzomys fulgens for one of the Mexican animals. Several other related species were described from the early 1890s onwards and in 1901 Clinton Hart Merriam united many of those into a palustris-mexicanus group of species, which also included the marsh rice rat. Edward Alphonso Goldman revised North American Oryzomys in 1918 and consolidated many forms into a single species Oryzomys couesi, with ten subspecies distributed from southern Texas and western Mexico south to Costa Rica. He placed it in an Oryzomys palustris group with the marsh rice rat and several species with more limited distributions, which he regarded as related to O. couesi but distinctive enough to be classified as separate species. In the 1930s, a few more forms related to O. couesi were described. As then recognized, the ranges of the marsh rice rat, a United States species, and Oryzomys couesi meet in southern Texas. In 1960, Raymond Hall reviewed