Comparisons.—From P. l. longicaudatus, brevicauda differs in: upper parts Tawny instead of Ochraceous-Buff; lower premolar with four instead of three counterfolds; m3 only, instead of both m1 and m3, with two counterfolds. From P. l. boimensis, brevicauda differs in: upper parts Tawny instead of Ochraceous-Orange; aristiforms wider; m3 with two instead of three counterfolds.
Specimens examined.—Total number, 3 (DZ), from Brazil, Amazonas, João Pessoa, Rio Juruá.
Proechimys longicaudatus boimensis J. A. [Allen]
Proechimys boimensis [Allen], 24 July, 1916, Bull. Amer. Mus. Nat. Hist., 35(27):523; [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.
Proechimys cayennensis [Osgood], 1944, Zool. Ser. Field Mus. Nat. Hist., 29(13):199.
Type locality.—Boim, Rio Tapajoz, Santarem, Pará, Brazil. Type: American Museum of Natural History, no. 37486, adult male; "October 10, 1911 (ex Museu Goeldi)."
Range.—Along lower course of Tapajoz River.
Diagnosis.—Upper parts Ochraceous-Orange; incisive foramen posteriorly constricted; mesopterygoid fossa sharply pointed anteriorly; p4 with four counterfolds, remaining molariform teeth with three counterfolds.
Pelage.—Aristiforms on middorsal region: Gray basally, gradually blackening toward tip which is extended as a long filament; total length, 16 to 18 mm; maximum width, 0.5 mm. Setiforms on middorsal region: Gray basally, gradually blackening toward tip, but interrupted by short (1.5 mm), Ochraceous-Orange, subapical zone; total length 18 to 20 mm; maximum width 0.09 mm. Setiforms on outer thighs: White basally, gradually blackening toward tip but interrupted by Ochraceous-Orange, or Ochraceous-Buff, subapical zone 3.5 mm long; total length 15 to 17 mm; maximum width, 0.06 mm.