_General characters._--Size medium; tail approximately same length as head and body; aristiforms moderately wide; feet rather large; ears of medium size; color on upper parts and sides sepia gradually changing to Ochraceous-Tawny; few differentiated, light-colored aristiforms present on outer thighs and rump; under surface of body and inner sides of legs white; tail with white tip and conspicuous, white pencil; feet white dorsally; skull short and smooth, somewhat flattened in interorbital region; jugals narrow dorso-ventrally; incisive foramen moderately long and notably narrow; vomerine sheath complete and slender; postorbital process of zygoma spinelike and involving mostly jugal; premolars usually with two counterfolds; molars with only one counterfold, rarely two in M1 or in M3. _Remarks._--The specimens available are undoubtedly faded and, therefore, the colors mentioned above for the upper parts and sides may not correspond to the colors of unfaded pelages. Desmarest (1817:59) describes the color of setosus as similar to that of the "Echimys de Cayenne" (_Proechimys guyannensis_) but being more "rousse." Is. Geoffroy Saint-Hilaire (1840:52) describes the same animal as being "d'un brun roussâtre" on the upper parts. The _Proechimys_ from Lagoa Santa, Minas Gerais, _"Echimys" elegans_ Lund, is certainly related to _P. iheringi_ as well as to _P. albispinus_. From _P. iheringi_, _elegans_ differs in having a smaller skull with shorter rostrum, narrower incisive foramen, and orthodont incisors. On the other hand the restricted distribution of the aristiforms in the pelage and the white, penicillate tail are points of resemblance to _iheringi_. From _P. albispinus_, _elegans_ differs in having a less spinous pelage and longer tail with white pencil instead of a brown pencil. The skulls, however, are similar, except for the fact that _elegans_ does not have proodont incisors as _albispinus_ sometimes does. Thomas (1921:141) states, after describing the skull of the type of _setosus_, that "Specimens corresponding to this animal have been obtained at Lagoa Santa, Minas, by Lund and others, and at Bahia." Thomas, however, would not have referred to specimens from "Bahia" as being comparable to _elegans_ had they not been different from _albispinus_ which he discussed in the same paper. Also, he would not have confused "specimens comparable to _elegans_" with a subspecies of _P. iheringi_ (_P. i. denigratus_, from southern Bahia) which has opisthodont instead of orthodont incisors. Since French collectors sent material to Europe at the beginning of the 19th century from (southern?) Bahia, possibly _setosus_ came from there.