Teeth.—Upper molariform teeth with three counterfolds each. Lower premolar with three counterfolds; molars with only two.
Comparisons.—From P. g. warreni, arabupu differs in: Narrower aristiforms; narrower incisive foramen; lower premolar with three instead of four counterfolds; lower molars with two, instead of three, counterfolds. From P. g. oris, arabupu differs in: Aristiforms wider; posterior margin of incisive foramen farther from plane of premolars; upper parts dark (15'j) Ochraceous-Tawny, instead of Ochraceous-Orange.
Remarks.—The sample is fairly uniform.
Specimens examined.—Total number, 6 (AMNH), from Brazil, Territorio do Rio Branco, Boa Vista, Mount Roraima, Arabupu; approximately 1540 m. altitude.
Subgenus TRINOMYS [Thomas]
Genotype.—Echimys albispinus Is. [Geoffroy] Saint-Hilaire, 1838; by original designation.
Trinomys [Thomas], July 1921, Ann. Mag. Nat. Hist., 8 (ser. 9):140 (orig. descr.); [Tate], 1935, Bull. Amer. Mus. Nat. Hist., 68(5):401; [Ellerman], 1940, The families and genera of living rodents, Brit. Mus. (Nat. Hist.), 1:115.