and Timothy Lawlor judged the differences between cozumelae and mainland couesi trivial and found that cozumelae was inside the range of variation of mainland Oryzomys populations; accordingly, they demoted the island form to a subspecies. Mark Engstrom and colleagues, writing in 1989, reaffirmed this conclusion. For an island form, this population is highly genetically variable. In its Cytb sequence data, it falls among populations of nominate couesi. Oryzomys couesi is also found on Turneffe Atoll off the coast of Belize and Roatán off Honduras. The Oryzomys of the eastern lowlands of Nicaragua was described as a separate species, Oryzomys richmondi, by Merriam in 1901, and Goldman retained it as a subspecies of O. couesi on the basis of its distinctly dark fur. In reviewing Nicaraguan Oryzomys in 1986, Jones and Engstrom did not keep richmondi as separate, because they thought the difference in color too small for the recognition of subspecies. Oryzomys dimidiatus, a small, dark Oryzomys with gray underparts, occurs with O. couesi in southeastern Nicaragua. According to Jones and Engstrom, rice rats from the island of Ometepe in Lake Nicaragua are distinctive in their large skull and small external measurements, with an especially short tail, soft fur that is orange-brown above and buffish below, and lack of sphenopalatine vacuities (openings in the roof of the mesopterygoid fossa, the gap behind the end of the bony palate). They considered that this population probably represented a separate subspecies, but declined to propose a new name because they had only one adult specimen. In Nicaragua, O. couesi occurs up to an altitude of . Costa Rica, Panama, and Colombia Oryzomys from Costa Rica have historically been referred to O. c. couesi, but Hanson and colleagues found that two specimens from Refugio Nacional de Vida Silvestre Mixto Maquenque, northeastern Costa Rica, differed as much from other O. couesi (11.93% Cytb sequence divergence) as O. couesi differed from the marsh rice rat (11.30%). They suggested that these animals represented a species distinct from O. couesi, but were unable to resolve the correct name for the species because they could not examine samples of dimidiatus or richmondi. Oryzomys is rare in Panama. Panamanian Oryzomys were first described by Goldman in 1912, who introduced the name Oryzomys gatunensis for a specimen from Gatún in the Canal Zone. In 1918, Goldman kept the animal as a separate species, remarking that it was similar to richmondi, but