May, 1913. New Peruvian Mammals — Osgood. 97 



293 ; hind foot 45. Skull of type: Basal length 67.5 ; occipito-nasal length 

 66.5; interorbital constriction 18.9; nasals 28.8 x 7.2; palate length from 

 gnathion 40.2; front of canine to back of M ^ 20.3; M ^ to M ^ 11.6. 



Remarks. M. canus is markedly different from all the known forms 

 of the opossum series except M. grisescens from which it differs in having 

 the usual white-tipped tail and in having all its paler markings less 

 suffused with fulvous. It is perhaps the palest member of the genus, 

 whereas M. andersoni, found at no great distance, is the most richly 

 colored. 



Oryzomys polius sp. nov. 



Type from Tambo Carrizal, mountains east of Balsas, Peru. Alti- 

 tude about 5000 ft. No. 19765 Field Museum of Natural History. 

 Adult female. Collected May 18, 191 2, by W. H. Osgood and 

 M. P. Anderson. 



Characters. A large, long-tailed species, of a grayish type of colora- 

 tion strongly suggesting various United States species of Neotoma. 

 Upper parts smoke gray tinged with fawn mesially and mixed uniformly 

 with dusky ; under parts grayish white, the hairs with slaty bases except 

 on the chin; eyelids blackish; ears thinly haired, blackish; hands and 

 feet, with carpal and tarsal joints, white; tail very finely annulated and 

 clothed with fine short hairs, white below and on sides, dusky above. 



Skull rather elongate; rostrum broad and heavy but relatively long; 

 nasals long but broad; supraorbital edges elevated and trenchant, 

 continuous with parietal ridges to occipito-squamosal suture; palate 

 with' deep lateral channels running from the anterior foramina to the 

 posterior lateral pits which are exceptionally large and deep; anterior 

 palatine foramina very large, extending posteriorly nearly to plane of 

 middle of first molar; mesopterygoid fossa obtusely pointed anteriorly, 

 extending slightly beyond the posterior plane of the last molar; molar 

 teeth of moderate size and normal pattern. 



Measurements. Very old female : Total length 352; head and body 

 164; tail 188; hind foot 30. Type: Total length 337; head and body 

 157; tail 180; hind foot 30. Skull of type and very old female, respec- 

 tively: Greatest length 34.7, 37; basilar length 27.1, 29.3; zygomatic 

 width 17.8, 19.3; least interorbital width 5.2, 5.8; nasals 14.2 x 4.2, 1 5.1 

 X 4.7; interparietal 10.2 x 3.4, 9.8 x 4.3; anterior palatine foramina 8.3 x 

 3, 9 X 3.7; postpalatal length 12.5, 13.5; upper toothrow 5.6, 5.4. 



Remarks. This species is not closely related to any with which I 

 have been able to compare it, and of the numerous descriptions of species 

 in this genus I do not find any which seem to indicate that it has received 



