Palmer in 1904[6] and the next year, Oldfield Thomas of the British Museum of Natural History described this animal as the holotype of a new species he named Nectomys dimidiatus.

[11] Hershkovitz also noted that while O. dimidiatus resembles a juvenile Nectomys in external anatomy, it is otherwise similar to the marsh rice rat (Oryzomys palustris).

[12] A second specimen was obtained in 1966 and the find was published in 1971 by Hugh Genoways and Knox Jones, who noted that the species is closely similar to O. palustris.

[18] Many aspects of the systematics of the O. couesi section remain unclear and it is likely that the current classification underestimates the true diversity of the group.

[24] Oryzomys dimidiatus is a medium-sized rice rat, smaller than O. couesi, with thick, lustrous fur and velvety underfur.

The hindfeet show small interdigital webs, but they lack long tufts of hair on the digits and some of the pads are reduced or absent.

[25] Compared to that of Nectomys, the skull is lightly built and has narrow nasals and a broad, round braincase without conspicuous ridges on it.

[28] Oryzomys dimidiatus is known from three specimens collected in the lowlands of the South Caribbean Coast Autonomous Region in southeastern Nicaragua.

[29] The first, an old male, was collected on November 5, 1904, in a banana plantation with very moist red clay on the Río Escondido near El Rama.

[6] The second, a young adult male, was caught on July 26, 1966, in dense cane on the south bank of the Río Mico at El Recreo, 15 km (9 mi) west from the location of the first specimen, along with three other rice rats (O. couesi, Melanomys caliginosus, and Oligoryzomys fulvescens), the cotton rat Sigmodon hirsutus, and the cottontail rabbit Sylvilagus brasiliensis.

[31] The 2019 IUCN Red List assessed the conservation status of Oryzomys dimidiatus as "Data Deficient", noting that very little is currently known about the species.