_Diagnosis._--Aristiforms wide; P4 and M1 with two counterfolds; p4 with two counterfolds, one anterior to main fold. _Pelage._--_Aristiforms on middorsal region_: Gray basally, gradually blackening toward tip; total length, 18 to 20 mm; maximum width, 0.8 mm. _Aristiforms on outer thighs_: Color much faded; total length, 15 to 17 mm; maximum width, 0.3 mm. _Setiforms on middorsal region_: Color faded; total length, 16 to 18 mm; maximum width, 0.04 mm. _Setiforms on outer thighs_: Color faded; total length, 10 to 13 mm; maximum width, 0.03 mm. [Illustration: FIGS. 129-132. _Proechimys setosus elegans_, sex ?, UZM no. L 104, Lagoa Santa. × 1.] _Skull._--Short; rostrum short and stout; length of nasals approximately 15 mm (broken); bullae roundish, smooth and well-inflated; jugals dorso-ventrally narrow (3.1 mm) with strong transverse ridge; postorbital process of zygoma spiniform, slender and involving mostly jugal; incisive foramen narrow (3.8 x 1.7 mm) and narrowest in posterior part; vomerine sheath complete; posterior palatine foramina obsolete; mesopterygoid fossa extending forward as far as middle of second molars. _Teeth._--Incisors orthodont. P4 with two counterfolds; M1 with two counterfolds but anterior one notably small; M2 and M3 with only one counterfold each. In lower jaw: p4 with two counterfolds, one anterior to main fold; molars with only one counterfold. _Comparisons._--From _P. s. elegans_, _setosus_ differs in: M1 with two counterfolds as opposed to only one; M3 with one counterfold instead of sometimes with two counterfolds; p4 with one counterfold anterior to main fold and another posterior, instead of both counterfolds posterior. _Remarks._--The measurements above were taken from the Maximilian specimen mentioned above. Measurements of the type were given by Desmarest as: head and body, 5-1/2 inches, tail about 6-1/2 inches. Is. Geoffroy Saint-Hilaire (1838:886) corrects these measurements to: head and body 195 mm; tail (part missing), 170 mm. =Proechimys setosus elegans= (Lund) _E[chimys]. elegans_ Lund, 1841, Kong. Danske Videnskab. Selsk. natur-vidensk. math. Afhandl., Kjöbenhavn, 8:99 (orig. descr.). _Loncheres elegans_ Lund, 1841, Kong. Danske Videnskab. Selsk, natur-vidensk. math. Afhandl., Kjöbenhavn, 8:245, 266, 294; Wagner, 1843, Wiegman's Archiv f. Naturg., Berlin, 2 (Jahrg. 9):47. _Echimys cayennensis_ Waterhouse, 1848, Nat. Hist., Mammalia, 2:337. _Echinomys cajennensis_ Winge, 1888, Jordfundne og nulevende Gnavere (Rodentia), E Museo Lundii, Kjöbenhavn, 1(3):71, pl. 6, figs. 5-6, pl. 7, fig. 1. _Proechimys setosus_ Thomas, 1921, Ann. Mag. Nat. Hist., 8 (ser. 9):141.