7. (_a_) No clavate aristiforms, tail with white tip, _P. setosus_, p. 384 (_b_) Clavate aristiforms among the ordinary ones, tail without white tip _P. albispinus_, p. 388 [Illustration: FIG. 22. Map showing the distribution of the two subgenera of the genus _Proechimys_.] [Illustration: FIG. 23. Map showing the geographic ranges of four species of the genus _Proechimys_.] [Illustration: FIG. 24. Map showing the geographic ranges of four species of the genus _Proechimys_.] 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.