Genus Proechimys J. A. [Allen]
Genotype.—Echimys trinitatis [Allen] and Chapman, by original designation.
Proechimys [Allen] and Chapman, 26 December 1899, Bull. Amer. Mus. Nat. Hist., 12(20):264, orig. description; [Tate], 1935, Bull. Amer. Mus. Nat. Hist., 68(5):398; [Ellerman], 1940, The families and genera of living rodents, Brit. Mus. (Nat. Hist.), 1:115.
General characters.—Muriform echimyids of medium size; pelage with flattened and lanceolate and sometimes clavate aristiforms, varying greatly in width and distributed over most of the dorsal surface from shoulders to hips or base of tail; setiforms also flattened, evenly distributed throughout; entire ventral surface and inner sides of legs white or, rarely, invaded by some buffy color; tail shorter than, equal to, or slightly longer than, head and body, bicolored and with a few bristles between scales, sometimes heavily penicillated; feet long and narrow; pollex rudimentary; hallux shorter than fifth toe; ears wide and long; mammae 2-1=6.
Skull.—Generally elongate and strongly built, with supraorbital ridges well developed, frequently extending across parietals toward occipital region; zygomatic arches variable in depth, always with postorbital process; infraorbital foramen with or without lower groove for transmission of nerve; incisive foramen usually large; vomerine sheath complete or incomplete; mesopterygoid fossa extending forward at least to plane of third molars; bullae large; angular process of mandible turned upward.
Figs. 18-21. Occlusal views of the upper left and lower right molariform teeth of the two subgenera of the genus Proechimys. Anterior end of the tooth row at the top of drawing. All × 6.
Figs. 18-19. Proechimys (Proechimys) goeldii steerei, sex ?, USNM no. 105537, "Hyutanaham." Upper teeth at left (fig. 18).