_Comparisons._--From _P. i. bonafidei_ and _P. i. gratiosus_, _iheringi_ differs in: Incisive foramen shorter; vomerine sheath complete, instead of usually incomplete; setiforms Cinnamon-Buff, instead of Ochraceous-Buff; upper molariform teeth with two or three separate counterfolds, instead of having counterfolds fused or reduced to one or two; aristiforms narrower in _iheringi_ than in _bonafidei_. _Specimens examined._--Total number, 25, from Brazil, as follows: São Paulo, _Formosa_, Ilha de São Sebastião, 9 (DZ 6, MN 2, MCZ 1); São Paulo, _Mogi das Cruzes_, Alto da Serra, alt. 900 m., 2 (DZ); São Paulo, _Ubatuba_, alt. 10 m., 4 (2 DZ, 2 MN); Rio de Janeiro, _Angra dos Reis_, 2 (MN); Rio de Janeiro, _Angra dos Reis_, Ilha Grande, 7 (5 DZ, 1 MCZ, 1 MN). =Proechimys iheringi bonafidei= subspecies nova _Type locality._--Fazenda Bõa Fé, _Teresópolis_, Rio de Janeiro, Brazil; alt. 850 meters. _Type_: Museu Nacional, no. 6183, adult male; collected on 18 August, 1942, by G. Pereira; SEPFA no. M 14663. _Range._--Known only from the type locality. _Diagnosis._--Aristiforms wide and stiff; tail shorter than head and body; setiforms Ochraceous-Buff; incisive foramen long; vomerine sheath incomplete, or rarely complete; molariform teeth with two counterfolds usually fused. _Pelage._--_Aristiforms on middorsal region_: Gray basally, gradually blackening toward tip; total length, 22 to 26 mm; maximum width, 0.8 mm. _Aristiforms on outer thighs_: Gray basally, gradually blackening toward tip but interrupted by Ochraceous-Buff subapical zone; some Ochraceous-Buff to tip; total length, 18 to 20 mm; maximum width, 0.7 mm. _Setiforms on middorsal region_: Gray basally, gradually blackening toward tip but interrupted by Ochraceous-Buff, subapical zone; total length, 17 to 20 mm; maximum width, 0.06 mm. _Setiforms on outer thighs_: Gray basally, gradually blackening toward tip but interrupted by Ochraceous-Buff, subapical zone; only a short blackened tip. _Skull._--Large, with elongate rostrum; bullae large and well inflated; jugals with transverse ridge inconspicuous; postorbital process of zygoma small, formed mostly by squamosal; incisive foramen elongated (5.5 × 2.5 mm); vomerine sheath incomplete or, if complete, with maxillary part thin and delicate; posterior palatine foramen at plane of first molars; mesopterygoid fossa extending forward as far as middle parts of second molars.