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.