Part 16

Type locality.--Arabupu, Mount Roraima, Bõa 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.

Teeth.--Upper molariform teeth with three counterfolds each. Lower premolar with three counterfolds; molars with only two.

Comparisons.--From P. g. warreni, arabupu differs in: Narrower aristiforms; narrower incisive foramen; lower premolar with three instead of four counterfolds; lower molars with two, instead of three, counterfolds. From P. g. oris, arabupu differs in: Aristiforms wider; posterior margin of incisive foramen farther from plane of premolars; upper parts dark (15'j) Ochraceous-Tawny, instead of Ochraceous-Orange.

Remarks.--The sample is fairly uniform.

Specimens examined.--Total number, 6 (AMNH), from Brazil, Territorio do Rio Branco, Bõa Vista, Mount Roraima, Arabupu; approximately 1540 m. altitude.

Subgenus =TRINOMYS= Thomas

Genotype.--Echimys albispinus Is. Geoffroy Saint-Hilaire, 1838; by original designation.

Trinomys Thomas, July 1921, Ann. Mag. Nat. Hist., 8 (ser. 9):140 (orig. descr.); Tate, 1935, Bull. Amer. Mus. Nat. Hist., 68(5):401; Ellerman, 1940, The families and genera of living rodents, Brit. Mus. (Nat. Hist.), 1:115.

General characters.--Pelage of upper parts with lanceolate and, sometimes, clavate aristiforms extending over most of rump and onto thighs; tail 86 to 103 per cent of length of head and body; tail sometimes white-tipped and sometimes penicillate; skull small, with ridges moderately developed; supraorbital ridges involving no part of parietals; infraorbital foramen with no separate groove for transmission of nerve; mesopterygoid fossa extending forward to level of second or first molars; incisors opisthodont, orthodont or proodont; molariform teeth, in occlusal view, with main fold large and usually reaching opposite wall; no counterfold anterior to main fold in upper molariform teeth and usually no counterfold posterior to main fold in lower molariform teeth; premolars larger than first molars, first molars larger than second molars and second molars larger than third molars; four molariform teeth of nearly equal size in some animals.

Thomas (1921:140) erected the subgenus Trinomys, including in it the species albispinus and setosus and stated that "the primary distinction between these [Trinomys and Proechimys] lies in the number of laminae present in the cheekteeth--four in Proechimys, three in Trinomys." The distinction is valueless as a subgeneric character, not only because the character is not constant in the species in the subgenus but also because there is subspecific variation in number of laminae in the cheekteeth. Proechimys albispinus, however, shares with three other species common characters, as listed above, and the name Trinomys will, therefore, apply to this group of species, since Proechimys albispinus is the genotype.

=Proechimys dimidiatus= (Günther)

Echimys dimidiatus Günther, 1 April 1877, Proc. Zool. Soc. London, 1876(4):747.

Proechimys dimidiatus Allen, 1899, Bull. Amer. Mus. Nat. Hist., 12(20):264; Ribeiro, 1905, Arch. Mus. Nac. Rio de Janeiro, 13:187; Thomas, 1921, Ann. Mag. Nat. Hist., 8 (ser. 9):141; Tate, 1935, Bull. Amer. Mus. Nat. Hist., 68(5):400; Ellerman, 1940, The families and genera of living rodents, Brit. Mus. (Nat. Hist.), 1:122.

Type locality.--Unknown; probably southwestern Rio de Janeiro, Brazil (see Remarks). Type: British Museum (Nat. Hist.), no. 51.7.21.24; presented by Lord Derby.

Range.--Rio de Janeiro, from the southern limit of the state northward to and including the Distrito Federal.

General characters.--Size large; tail averaging 80 per cent of head and body; aristiforms narrow and soft (0.4 to 0.5 mm wide), imparting a non-spiny character to the pelage; general color of upper parts Ochraceous-Buff, finely lined with blackish brown, gradually becoming lighter on sides; ventral surface of body and inner sides of legs white; feet dorsally white but with a sepia-colored stripe along outer margin; tail brownish-black above and white below, but white sometimes extended to upper side in distal part; skull broad with no conspicuous ridges; jugals deep with transverse ridge usually conspicuous; postorbital process of zygoma involving only squamosal; incisive foramen short and wide posteriorly; vomerine sheath complete in 95 per cent of specimens and with maxillary part thick; posterior palatine foramina at plane of first molars or slightly anterior to them; bullae moderately developed; in juvenal specimens, each upper molariform tooth with three counterfolds, but posteriormost counterfold small; in adult specimens, posteriormost counterfold disappearing in 50 per cent of fourth premolars and first molars, in 20 per cent of second molars, and in 15 per cent of third molars; lower molariform teeth with two counterfolds in almost every juvenal specimen, this number, in adult animals, decreasing in m3 to one in 20 per cent of specimens but rarely being reduced in other teeth.

General characters.--Aristiforms soft and narrow, ranging from 15 to 19 mm in total length and 0.4 to 0.5 mm in maximum width; pelage generally non-spiny and not harsh; length of tail ranging from 20 per cent shorter than head and body to as long as, or slightly longer than, head and body; ears rather small (23 to 25 mm).

Color.--General color of back and sides results from uniform mixture of black distal parts of aristiforms with Ochraceous-Buff of subapical zone of setiforms. Dorsally, from nose caudad to rump, mixture appears brownish-black, lined with Ochraceous-Buff; toward sides, amount of Ochraceous-Buff gradually increases and resultant color is much lighter brown than on back. On outer parts of arms and legs, color turns gradually to sepia toward distal parts and finally to uniform sepia on wrists and ankles, this color extending to outer dorsal parts of hands and feet; on ankles, sepia forms complete ring, as usual in the genus. Tail blackish-brown on upper parts, this stripe gradually tapering toward tip where dark brown hairs form small pencil; white of under side of tail sometimes seen also entirely around distal part, short of tip which remains dark brown. Ventral surfaces wholly white, from upper lips caudad including inner surfaces of legs.

Hairs.--Aristiforms on middorsal region: Gray basally, gradually blackening toward tip that has long, fine filament; total length 16 to 19 mm; maximum width 0.5 mm. On outer thigh whitish basally, gradually blackening toward tip; some with Ochraceous-Buff, subapical zone; total length 13 to 15 mm; maximum width 0.25 mm. Setiforms on middorsal region: Whitish on basal half, gradually blackening toward tip, but interrupted by Ochraceous-Buff, subapical zone; some with Light Ochraceous-Buff, subapical zone and short, blackish zone on tip; total length 12 to 14 mm; maximum width 0.02 mm. Setiforms on outer thighs: Whitish on basal half, then gradually becoming gray on middle part and finally Light Ochraceous-Buff on distal third, or with tip blackish and Ochraceous-Buff, subapical zone.

Skull.--Elongate and broad with no conspicuous crests; rostrum rather stout; jugals deep with transverse crest usually well-developed; zygomatic postorbital process conspicuous and formed entirely of squamosal; incisive foramen short and wide posteriorly; vomerine sheath complete in great majority of specimens, its maxillary part wide and strong; posterior palatine foramina on plane with front of M1 or slightly farther forward; bullae rather small and elongate.

Teeth.--P4 with three secondary folds in all juvenal specimens, but posteriormost fold small and disappearing in 50 per cent of adult specimens; M1 with 3 outer folds in juveniles and also disappearing in 50 per cent of adults; M2 with three outer folds in juveniles, but only 20 per cent remaining in adults; M3 with 3 outer folds in 50 per cent of juveniles, decreasing to 15 per cent in adults. Lower molariform teeth: p4 with 2 secondary folds; m1 with 2 secondary folds in 90 per cent of adults and in all juveniles; m2 with 2 secondary folds in 98 per cent of adults and in all juveniles; m3 with 2 secondary folds in 81 per cent of adults, remaining percentage with only one counterfold, and with 2 secondary folds in all juveniles.

Remarks.--Samples studied of P. dimidiatus are notably uniform throughout the geographic range of the species. The few biotypes detected seemed unworthy of subspecific rank.

In discussing the type locality of the species, Thomas (1921:141) states: "We know that its donor did obtain a number of specimens from Rio Janeiro, and the skull agrees so closely with those of two examples from Itatiaia, near to the Rio-Minas frontier, collected and presented by Prof. J. P. Hill, that I have no hesitation in referring the latter to Günther's species."

Specimens examined.--Total number, 211 (MN), from Brazil as follows: Rio de Janeiro; Parati, Pedra Branca (400 m.), 113; Mangaratiba, Fazenda do Rubião (750 m.), 3; Fazenda do Tenente (700 m.), 4; Fazenda da Lapa (450 m.), 13; Teresópolis, Fazenda Guinle (960 m.), 61; Nova Iguassú, Barro Branco (20 m.), 16; Distrito Federal, Tijuca, 1.