Subgenus Proechimys J. A. [Allen]
General characters.—Pelage with lanceolate aristiforms limited to an area on the dorsal surface between the shoulders and the hips; length of tail less than 90 per cent of length of head and body; skull with conspicuous ridges; extension of supraorbital ridges always evident on parietals; infraorbital foramen usually with separate groove for transmission of nerve; palate usually extended posteriorly as far as third molars; incisors opisthodont; molariform teeth with a small main fold, never extended transversely to opposite wall in occlusal surface of tooth; usually one counterfold anterior to main fold in upper molariform teeth and posterior to main fold in lower molariform teeth; premolars usually smaller than first molars, first molars smaller than second molars but second molars larger than third molars.
Proechimys goeldii [Thomas]
General characters.—Size large; tail short; aristiforms narrow and soft, usually concealed in pelage by setiforms; general color of upper parts some tint of orange, gradually becoming lighter on sides with no conspicuous, dark longitudinal band on back; feet dark; ventral surface of body and inner side of legs white but sometimes with some buff locally; skull broad and strongly built but not conspicuously ridged; zygomatic expanse great and rostrum not elongate; incisive foramen narrow; bullae large and inflated; upper molariform teeth with three to four counterfolds, M3 ordinarily with four; lower premolars with four, and molars with three, counterfolds.
Proechimys goeldii steerei Goldman
Proechimys steerei Goldman, Proc. Biol. Soc. Washington, 24:238, 28 November 1911 (original description); Goldman, 1912, Proc. Biol. Soc. Washington, 25:186; [Tate], 1935, Bull. Amer. Mus. Nat. Hist., 68(5):400; [Ellerman], 1940, The families and genera of living rodents, Brit. Mus. (Nat. Hist.), 1:119; [Osgood], 1944, Zool. Ser. Field Mus. Nat. Hist., 29(13):204.
Type locality.—Hyutanaham, Upper Purus, Lábrea, Amazonas, Brazil. Type: United States National Museum, no. 105535, adult male; collected in 1901 by Prof. J. B. Steere.
Range.—Known only from the type locality and Porto Velho.
Diagnosis.—Upper parts Mars Orange on back, grading to Ochraceous-Tawny on sides; zygomatic breadth narrow; nasals short; incisive foramen narrow and short; vomerine sheath complete and thick; upper molars usually with four counterfolds.
Pelage.—Aristiforms on middorsal region: Grayish basally, gradually blackening toward tip; total length, 16 to 19 mm; maximum width, 0.5 mm. Setiforms on middorsal region: Grayish on basal third, gradually blackening toward tip but interrupted by a Mars Orange, subapical zone 1.5 mm long; total length, 16 to 19 mm; maximum width, 0.06 mm. Setiforms on outer thighs: Whitish basally, gradually blackening toward tip but interrupted by Orange Rufous or Ochraceous-Tawny, subapical zone; total length, 14 to 16 mm; maximum width, 0.05 mm.