======================+=========+==========+========+=========+======= | Number | | Length | | Length AGE | of | Weight | of head| Length | of | cheek- | in grams | and | of tail | hind | teeth | | body | | foot ----------------------+---------+----------+--------+---------+------- One day old | 2 | 20.5 | 70 | 53 | 24 17 days old | 2 | 26.0 | 110 | 60 | 28 Juvenile | 2 | 85.0 | 150 | 105 | 39 Adolescent | 3 | 115.0 | 175 | 120 | 45 Adolescent (older) | 3 | 180.0 | 195 | 135 | 45 Adult | 4 | 200.0 | 223 | 158 | 48 Senile individual | 4 | 360.0 | 230 | 170 | 48 ----------------------+---------+----------+--------+---------+------- The weights and measurements (except for one- and 17-day-old animals) represent averages of specimens of the different ages. 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. [Illustration: 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.