are classified as the subspecies aquaticus, which was described as a separate species, Oryzomys aquaticus, in 1891. Here the range of O. couesi meets that of the marsh rice rat; in parts of Kenedy, Willacy and Cameron counties, Texas, and in far northeastern Tamaulipas, the two are sympatric (occur in the same places). In the contact zone, couesi occurs further inland, while the marsh rice rat lives along the coast. In experimental conditions, the two fail to interbreed and genetic analysis yields no evidence of gene flow or hybridization in the wild. Compared to populations further to the south, aquaticus is larger and paler and has a more robust skull. Specimens from Tamaulipas are slightly darker than those from Texas. The Cytb sequences of specimens of aquaticus form a separate group, but cluster among specimens of O. c. couesi from further south. The form peragrus is known from further south in Mexico, in the Río Verde basin of San Luis Potosi, the state of Hidalgo, and far northern Veracruz. Late Pleistocene fossils of this form have been found in Cueva de Abre, Tamaulipas. According to Goldman, it is intermediate in color between O. c. aquaticus and O. c. couesi, but has a skull similar to that of aquaticus. Goldman united populations ranging from northern Veracruz through eastern Mexico, Guatemala, Honduras, and Nicaragua south to far northwestern Costa Rica in the nominate subspecies, Oryzomys couesi couesi. He placed six other names as full synonyms of this form, which has its type locality in Guatemala—Oryzomys jalapae Allen and Chapman, 1897, from Veracruz; Oryzomys jalapae rufinus Merriam, 1901, from Veracruz; Oryzomys teapensis Merriam, 1901, from Tabasco; Oryzomys goldmani Merriam, 1901, from Veracruz; Oryzomys jalapae apatelius Eliot, 1904, from Veracruz; and Oryzomys richardsoni Allen, 1910, from Nicaragua. According to Goldman, individual variation within the subspecies is large, which has led to the large number of published synonyms, but populations from all parts of its range are essentially similar. The subspecies Oryzomys couesi pinicola was described in 1932 from a pine ridge in western British Honduras (now Belize); it is smaller and darker than nominate couesi, which also occurs in Belize, and has a more delicate skull. In 1901, Merriam described the Oryzomys of the island of Cozumel as a separate species, Oryzomys cozumelae, and Goldman kept it as such because of its large size, dark fur, and long tail. In 1965, however, Knox Jones