Fig. 98. Map showing the geographic ranges of the subspecies of Proechimys guyannensis in Brazil.
Comparisons.—From P. g. oris and P. g. hyleae, riparum differs in: Shorter and wider incisive foramen; vomerine sheath incomplete, instead of sometimes incomplete. From P. g. oris, riparum differs in: Upper parts Ochraceous-Tawny instead of Ochraceous-Orange; aristiforms conspicuously wider. From P. g. hyleae, riparum differs in: Aristiforms narrower; upper parts Ochraceous-Tawny instead of Tawny; lower premolars with three, instead of four, counterfolds; lower molars with two, instead of three, counterfolds.
Specimens examined.—Type only.
Proechimys guyannensis arabupu subspecies nova
Type locality.—Arabupu, Mount Roraima, Boa Vista, Territ. Rio Branco; about 1540 meters altitude. Type: American Museum of Natural History, no. 75816, adult male; collected by Dr. G. H. H. [Tate] on 30 December, 1927; original number, 4716.
Range.—Known only from the type locality.
Diagnosis.—Aristiforms conspicuously wide and stiff; color on upper parts dark, near (15'j) Ochraceous-Tawny; incisive foramen widest in anterior third; vomerine sheath complete, sometimes incomplete; upper molariform teeth and lower premolar with three counterfolds; lower molars with two counterfolds.
Pelage.—Aristiforms on middorsal region: Whitish basally, gradually blackening toward tip; total length, 19 to 22 mm; maximum width, 1.1 mm. Setiforms on middorsal region: Gray basally, gradually blackening toward tip but interrupted by dark (15'j) Ochraceous-Tawny, subapical zone 3 mm long; some completely blackish on distal parts; total length, 20 to 23 mm; maximum width, 0.07. Setiforms on outer thighs: Whitish basally, gradually blackening toward tip but interrupted by Ochraceous-Buff or Light Ochraceous-Buff, subapical zone; total length, 20 to 23 mm; maximum width, 0.07 mm.
Skull.—Size medium; nasals pointed posteriorly; supraorbital ridges prominent and slightly extended caudad onto anterior half of parietals; groove for transmission of nerve in infraorbital foramen weakly developed; zygomatic arches strong; postorbital process of zygoma involving mostly squamosal; incisive foramen approximately 5.5 × 2.7 mm, widest in anterior third and constricted posteriorly, with posterior margin about 1 mm anterior to plane of premolars; vomerine sheath complete, with premaxillary part expanded and maxillary part notably slender and sometimes lacking; mesopterygoid fossa in some specimens extending forward as far as middle parts of second molars; bullae large and inflated.