May, 1913. New Peruvian Mammars — Oscoon. 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. j 
Oryzomys polius sp. nov. 
Type from Tambo Carrizal, mountains east of Balsas, Peru. Alti- 
tude about so00o ft. No. 19765 Field Museum of Natural History. 
Adult female. Collected May 18, 1912, 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, 15.1 
X 4.7; interparietal 10.2 x 3.4, 9.8 x 4.3; anterior palatine foramina 8.3 x 
3, 9X 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 
