158 FIELD MUSEUM OF NATURAL HISTORY ZOOLOGY, VOL. X. 



Oryzomys minutus (Tomes). PIGMY ORYZOMYS. 



Two specimens, Mountains northeast of Otuzco, near head of Rio 

 Chicama. Altitude 10,000 feet. 



These are practically indistinguishable from specimens from the 

 south side of Mt. Pichincha, Ecuador, which may be regarded as prob- 

 ably typical of 0. minutus. They differ from O. dryas mainly in color, 

 being much duller and more grayish above, paler below, and with the 

 ears less blackish, and therefore in less contrast with the surrounding 

 parts. In cranial characters they are closely related only to 0. dryas 

 and differ from 0. stolzmanni and allies in having more delicately 

 formed skulls, with very small teeth, a non-projecting zygomatic plate, 

 and a full rounded relatively broad braincase. Whether these char- 

 acters can be detected in the immature type of 0. minutus will doubtless 

 remain uncertain until the type can be carefully compared with an 

 ample amount of pertinent material. 



Oryzomys dryas Thomas. 



Nine specimens: Mountains east of Balsas (3), Tambo Almirante, 

 near Uchco (i), Tambo Veiitija, near Molinopampa (5). 



These small mice were taken in dense forest where there was great 

 humidity but no very high temperature. In the flesh, they present a 

 very characteristic appearance, somewhat different from the normal 

 "pigmy Oryzomys" and resemble rather some of the full-furred Reithro- 

 dontomys of southern Mexico and Central America. Their soft woolly 

 pelage, richly ochraceous under parts, and sharply contrasted blackish 

 ears amply distinguish them without reference to cranial characters. 

 If not identical with typical 0. dryas from Ecuador, their departure from 

 it can only be very slight since they conform in every respect to the 

 original description of the species. 



The resemblance of this diminutive mouse both externally and 

 cranially to certain species of Rhipidomys is noteworthy. Its slender 

 hind foot and its laterally pitted palate are the only obvious objections 

 to stating that it is an exact minature, for example, of R. fulviventer. 

 If it had been chosen as the type of Oligoryzomys instead of the typically 

 oryzomyine 0. navus, some slight grounds might be urged for the 

 recognition of such a subgenus. 



Oryzomys laticeps nitidus Thomas. 



Twenty- two specimens : Lagunas (3) , Moyobamba ( 1 1 ) , Poco Tambo 

 (i), Tambo Yaku, near Rioja (6), Yane Yaku, near Yurimaguas (i). 



