_Type locality._--Lower Rio Solimões (up the Solimões 50 to 60 miles on the north bank of the river), _Manacaparú_, Amazonas, Brazil. _Type_: American Museum of Natural History, no. 37124, adult female; collected 20 April, 1914, by Leo E. Miller (Roosevelt Brazilian Expedition). _Range._--Known only from type locality. _Diagnosis._--Upper parts Tawny, with darker longitudinal band on back, gradually becoming Ochraceous-Buff on sides; zygomata widely spread; nasals long; incisive foramen long; vomerine sheath incomplete; only M3 with four counterfolds. _Pelage._--_Aristiforms on middorsal region_: Grayish basally, gradually blackening toward tip; total length, 18 to 20 mm; maximum width, 0.8 mm. _Setiforms on middorsal region_: Grayish basally, gradually blackening toward tip but interrupted by Tawny, subapical zone 2 mm long; total length, 18 to 20 mm; maximum width, 0.06 mm; some blackened toward tip without subapical zone. _Setiforms on outer thighs_: Whitish basally, gradually blackening toward tip but interrupted by Ochraceous-Buff, subapical zone 2.5 mm long; total length, 18 to 20 mm; maximum width, 0.05 mm. _Skull._--Large, elongate, and strongly built; rostrum not conspicuously elongated; nasals bluntly pointed posteriorly; supraorbital ridges wide and extending posteriorly across parietals almost to level of interparietal; infraorbital foramen with moderate development of groove for transmission of nerve; zygomatic arches slender; postorbital process of zygoma involving mostly squamosal; incisive foramen 6.5 mm long and 2.7 mm wide, wider in anterior third and gradually constricted posteriorly, with margins extended toward palate as ridges; vomerine sheath incomplete, maxillary part threadlike; mesopterygoid fossa extending forward as far as anterior third of m3; bullae large and well inflated. _Teeth._--P4 with three counterfolds; M3 with four counterfolds; M1 and M2 with three counterfolds. Lower premolars with four counterfolds; lower molars with three counterfolds. _Comparisons._--From _P. s. amphichoricus_, _kermiti_ differs in: upper parts Tawny instead of Buckthorn Brown; incisive foramen longer and wider; vomerine sheath incomplete; only M3 instead of usually all molars, with four counterfolds. From _P. s. liminalis_, _kermiti_ differs in: upper parts Tawny instead of Ochraceous-Tawny; aristiforms narrower; M3 only, instead of usually M2 and M3, with four counterfolds. _Specimens examined._--Only the type. =Proechimys longicaudatus= (Rengger)