ARBOREAL RICE RATS — HERSHKOVITZ 559 



AMNH, 1); Moutalvo, Rfo Bobonaza, Napo-Pastaza, 3 (CNHM); Rfo Pindo 

 Yacu, Napo-Pastaza, 5 (CNHM); Yana Rumi, Napo-Pastaza, 3 (CNHM); Capa- 

 huari, Napo-Pastaza, 2 (CNHM); Zamora, Santiago-Zamora, 4 (AMNH, in- 

 cludes type of melleus). 



Peru: Moyobamba, Amazonas, 1 (BM, type of osgoodi); Hacienda Exito, Rfo 

 Cayumba, Huanuco, 2 (CNHM); Satipo, Junfn, 1 (MCZ); La Pampa, Puno, 

 1 (kcZ); Quincemil, Cuzco, 3 (CNHM); Itahuania, Madre de Dios, 1 (CNHM); 

 Boca Colorado, Madre de Dios, 1 (CNHM). 



Oryzomys concolor roberti Thomas 



Rhijndomys roberti Thomas, Proc. Zool. Soc. London (1903), No. 2, p. 237, 1903. 

 [Oryzomijs {(Ecomys)] Roberti, Thomas, Ann. Mag. Nat. Hist., ser. 7, vol. 18, p. 



445, 1906. 

 CE[comys] roberti, Thomas, Ann. Mag. Nat. Hist., ser. 8, vol. 3, p. 378, 1909 



(comparison) . 

 Oecomys roberti, Vieira, 1945, Arq. Zool. Sao Paulo, vol. 4, p. 428, 1945 (Fazenda 



Aricd,, Rio Aried, Mato Grosso, Brazil). 

 Oryzomys {(Ecoviys) mamorae Thomas, Ann. Mag. Nat. Hist., ser. 7, vol. 18, p. 



445, 1906 (type locality, "Mosetenes," upper Rio Mamore, Yungas, Cocha- 



bamba, Bolivia). 

 CEcomys mamorae, Osgood, Field Mus. Nat. Hist., zool. ser., vol. 10, p. 206, 1916 



(Todos Santos, Rfo Chapar^, Cochabamba, Bolivia). 



Type: Adult male, skin and skull (BM 3.7.7.67) collected July 6, 

 1902, by Alphonse Robert. 



Type locality: Santa Ana de Chapada, Mato Grosso, Brazil; alti- 

 tude, 800 meters above sea level. 



Distribution: Northern Bolivia in the departments of Beni, 

 Cochabamba, Santa Cruz, and Chuquisaca west into Mato Grosso, 

 Brazil, in the Rio Paraguay basin; altitudinal range approximately 

 200 to 1,500 meters above sea level. 



Characters: Smaller and paler than superans; upperparts buffy 

 to tawny mixed with dark brown, underparts entirely white and 

 sharply defined from sides, or, sometimes, with a buffy or ochraceous 

 wash on chest and beUy ; skull with supraorbital ridges less developed 

 and divergent posteriorly than in other races. 



Measurements: See table 10. 



Variation: The type and two specimens at hand from Mato Grosso, 

 Brazil, are the palest representatives of the species east of the Andes. 

 Specimens from the Bolivian departments of Chuquisaca, Beni, and 

 Santa Cruz show a heavier mixture of dark brown on upperparts and 

 sides. Six specimens from Todos Santos, Rio Chapare, collected by 

 R. H. Becker, average nearly as dark on upperparts as superans. 

 The underparts, however, are pure white in two, more or less buffy 

 on belly and midline of chest in the others. 



Remarks: The clear white or buffy underparts distinguish every 

 member of roberti from superans. On the other hand, subspecies 

 roberti is hardly separable from Amazonian concolor by its paler color, 



