_Specimens examined._--Total number, 4, from Brazil as follows: Pará, _Faro_, Faro, Fazenda Paraiso, 2 (AMNH); Amazonas, _Manaus_, Manaus, 1 skull (AMNH); Amazonas, _Manaus_, Acajutuba, 1 (MN).
_Additional records._--Total number, 7 (British Museum), from Brazil, as follows: Pará, _Santarem_, Santarem (Thomas, 1912:89; 1920:277), 3; Amazonas, _Manaus_, Acajutuba (Thomas, 1920:277), 2; _Manacaparú_, Manacaparú (Thomas, 1920:277), 2.
[Illustration: FIGS. 33, 36. _Proechimys semispinosus liminalis_, female, MN no. 6253, Rio Quichito. Type. × 1.]
[Illustration: FIGS. 34, 37. _Proechimys semispinosus amphichoricus_, male, AMNH no. 77020, Mount Duida. Type. × 1.]
[Illustration: FIGS. 35, 38. _Proechimys semispinosus kermiti_, female, AMNH no. 37124, Lower Rio Solimões. Type. × 1.2 (from photograph).]
_General characters._--Size large; tail short and hairy; aristiforms wide and stiff, especially well-developed on back; general color on upper parts some shade of ochraceous, usually much darker on back and forming a conspicuous dorsal band; feet dark; ventral surfaces and inner sides of legs white; skull elongate and strong with ridges well developed; incisive foramen long and narrow; bullae large; usually four counterfolds in M3 and M2; usually three but sometimes four counterfolds in M1 and even P4; lower premolar with four and lower molars with three counterfolds.
[Illustration: FIGS. 39, 40. _Proechimys semispinosus liminalis_, female, MN no. 6253, Rio Quichito. Type. × 1.]
[Illustration: FIGS. 41, 42. _Proechimys semispinosus amphichoricus_, male, AMNH no. 77020, Mount Duida. Type. × 1.]
[Illustration: FIGS. 43, 44. _Proechimys semispinosus kermiti_, female, AMNH no. 37124, Lower Rio Solimões. Type. × 1.2 (from photograph).]
=Proechimys semispinosus liminalis= subspecies nova
_Type locality._--Rio Quichito, affluent from the south of the Javarí River, near _Benjamin Constant_, Benjamin Constant, Amazonas, Brazil. _Type_: Museu Nacional, no. 6253, adult female, collected in August, 1942, by E. Parko.
_Range._--Known only from the type locality.
_Diagnosis._--Color uniformly dark, setiforms marked with Ochraceous-Tawny; skull wide across zygomata; nasals short; prepalatilar part of skull long; incisive foramen long and narrow; vomerine sheath incomplete or complete; M2 and M3 almost always with four counterfolds; M1 more rarely with four counterfolds.