1901.] Allen, New South American Murida, etc. 4 7 



The skull and teeth present no differences of distinctive importance. Com- 

 pared with 0. magdalence, its nearest known ally, the skull is much broader 

 throughout, with the teeth of the molar series about one third broader. Total 



length, 34 ; basilar length, 21.6 ; zygomatic width, ; mastoid width, 13 ; 



postorbital width, 5 ; length of nasals, 13 ; palatal length, 8 ; palatal foramina, 

 5 ; length of upper toothrow, 5 ; length of lower jaw, 17 ; height at condyle, 

 8.6 ; lower toothrow, 5.8. 



This species is based on a series of n specimens, collected 

 by Mr. P. O. Simons at Perene, Department of Junin, Peru, at 

 an altitude of 800 m., in March and April, 1900. The series in- 

 cludes several young adults, which are darker, especially along 

 the median line above, with less of the yellowish brown of the 

 adults. One old male (No. 0-7-7-25) is much larger than the 

 rest of the series and of a rather deeper brown above. One 

 young example (No. 0-7-7-26) is exceptional for the strong wash 

 of pale yellowish brown on the sides. 



Externally this form is not readily distinguished from O. 

 magdalentz, but the two are easily separable on comparison of the 

 skulls. Both are apparently geographical forms of O. laticeps. 



Oryzomys rivularis, sp. nov. 



Type, No. 1-1-6-5, British Museum, ? adult, Rio Verde, northern Ecuador, 

 altitude 3200 feet, Nov. 28, 1899 ; collected by R. Miketta. 



In coloration throughout essentially like 0. bolivaris, but much larger and 

 with the tail much longer than head and body. 



Measurements (of type and only specimen). Total length, 238 mm. ; head 

 and body, in ; tail, 127 ; hind foot, 32 ; ear, 17. 



Skull narrow and slender, as in O. magdalenee , but the rostral portion still 

 more elongated and narrower, the zygomatic branch of maxilla broader, the 

 anterosuperior border more produced, and the enclosed foramen less expanded 

 laterally ; posterior palatal opening broader ; dentition weak, as in 0. magda- 

 lence. Total length, 32 ; basilar length, 23.6 ; zygomatic width, 15 ; mastoid 

 width, 12 ; postorbital width, 6 ; length of nasals, 7 ; length of palate, 7 ; 

 palatal foramina, 4 ; upper toothrow, 4.6 ; length of lower jaw, 17 ; height at 

 condyle, 8 ; lower toothrow, 5 mm. 



This form closely resembles O. bolivaris in coloration and in 

 the small size of the ears, in comparison with these members in 

 the O. laticeps group, and from which group it further differs 

 in the length of the tail, considerably exceeding that of the head 

 and body. Known at present only from the type, in which the 

 body is much overstuffed, it greatly exceeding the measurements 

 taken from the specimen in the flesh. 



