2 ID Bulletin American Museum of Natural History. [Vol. V, 



hairs over the middle of the dorsal region, lighter, more buffy yellow on the 

 sides ; below gray, with a slight buffy wash, the basal portion of the fur dusky 

 plumbeous. Line of demarcation between the coloration of dorsal and ventral 

 surfaces indistinct, often passing gradually the one into the other. Ears of 

 medium size (smaller than in either of the preceding species of this genus), 

 low, broad and very evenly rounded above, dusky, practically naked (pulver- 

 ulent) on both surfaces (under a lens the surface is shown to be covered with 

 very minute short whitish-tipped hairs). Feet above light grayish brown, with 

 a faint yellowish or buffy tinge, scantily haired ; palms and soles naked, the 

 former brownish flesh-color, the latter a little darker brown, 6-tuberculate. 

 Tail about one-fourth shorter than head and body, naked (clothed scantily with 

 hairs so minute as to be nearly invisible without a lens), indistinctly bicolor, 

 pale brown above, lighter, almost isabella color below for the basal two-thirds, 

 the line of demarcation between the two colors indistinct. 



Young. A very young example (probably a nursling) is uniform dusky 

 brown above faintly washed with yellowish gray, more distinct on the head, 

 and particularly on the sides of the head. Below similar but much paler. In- 

 side of ears well clothed with very short yellowish dusky hairs. Nearly full- 

 grown examples are variously intermediate between this and the fully adult 

 phase. 



Measurements (average of 10 adult males, taken in the flesh) : Total length, 

 265 (250-280) mm. ; head and body, 154 (141-161) ; tail, in (101-120) ; hind 

 foot, 28 (27-30) ; ear from crown, 15.3 (13-18). A similar number of females 

 average smaller, as follows : Total length, 235 (220-253) ; head and body, 142 

 (132-150) ; tail, 93 (86-105) ; hind foot, 26.6 (25-29). 



The skull is that of a typical Oryzomys (taking O. palustris as the type of 

 the genus), except as regards a few minor details, principally the form of the 

 interparietal, which is very narrow antero-posteriorly and very broad trans- 

 versely, as it is in most of the species of Oryzomys here described. An average 

 adult male skull measures as follows : Total length, 32.5 mm. ; basal length, 

 28.7 ; greatest zygomatic breadth, 17.3 ; greatest mastoid breadth, 12.5 ; least 

 interorbital breadth, 5.8; length of nasals, 13.5 ; antero-posterior breadth of 

 interparietal, 2.5 ; transverse breadth of same, 10.2 ; distance from incisors to 

 first molar, 8.9 ; length of anterior palatine foramen, 6.9 ; length of crown 

 surface of upper molar series, 4.5 ; length of lower jaw, 22.9 ; height of same 

 at condyle, 7.6. 



Type, No. ff^> $ ad., Princestown, Trinidad, April 12, 1893, coll. Frank 

 M. Chapman. 



This species is represented by a series of 38 specimens, nearly 

 all adults, but including one nursling, and a few others slightly 

 immature. Among the practically adult specimens the general 



