6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 60 



angular, with moderately developed supraorbital ridges and small 

 audital bullae. 



Color. — Upper parts near Mars brown of Ridgway, darkened 

 along the broad median line from top of head to base of tail, becom- 

 ing lighter, more rufescent on cheeks, shoulders and sides ; throat 

 grayish, rest of under parts usually overlaid with dark ochraceous 

 buff, but varying to dull white, the basal color of the fur everywhere 

 deep plumbeous ; nose and ears blackish ; outer sides of limbs dark 

 brownish, except a light buffy line extending from outer sides of 

 wrists posteriorly along lower edge of forearms ; fore feet blackish, 

 becoming lighter on the toes ; hind feet dark brown and thinly 

 clothed with short hairs to toes, the toes dark flesh color and nearly 

 naked, but with rather conspicuous tufts of silvery hairs projecting 

 beyond claws of four longest digits ; tail dark brown above, usually 

 somewhat paler below. 



Skull. — Similar in size to that of O. dez-ius, but more angular, 

 the zygomata more widely spreading, and supraorbital and temporal 

 ridges distinct; audital bullae decidedly smaller; dentition about the 

 same. Differing from those of 0. meridensis and 0. maculiventer 

 in much larger size and greater angularity. 



Measurements. — Type: Total length, 340 millimeters; tail verte- 

 brae, 185 ; hind foot, 38. Average of five adult topotypes, 314 (309- 

 322) ; 164 (159-170) ; 35.7 (34-37). Skull (type) : Greatest length, 

 37.8; condylobasal length, 34.5; zygomatic breadth, 20; nasals, 14; 

 interorbital breadth, 6; interparietal, 11.8 x 5; incisive foramina, 6; 

 length of palatal bridge, 7.8 ; maxillary toothrow, 5.9. 



Remarks. — Like the allied species — 0. devius, O. meridensis and 

 O. maculiventer — this large rice rat is an inhabitant of the mountains. 

 It was found only in the heavy forest at about 4,500 feet altitude 

 where precipitous slopes border the narrow canyon of the Rio 

 Limon. The animals live in holes under logs and rocks along steep 

 overhanging banks of the stream. The skull of O. pirrensis com- 

 bines the large general size of that of O. devius with the small audital 

 bullae of meridensis and maculiventer; it differs from both in the 

 development of the supraorbital and temporal ridges. O. meriden- 

 sis and O. maculiventer are evidently very nearly related, but com- 

 parison of three skulls of the former with four of the latter seems 

 to show that O. maculiventer differs in the smaller size of the inter- 

 parietal and heavier maxillary arm of zygoma. 



Specimens examined. — Eight, all from the type locality. 



