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



that due to wear, but the under parts range from dull gray to ochraceous 

 buff. A grayish white spot at the base of the ear is usually evident. 

 Average flesh measurements of ten adults are as follows: Total length 

 267 (258-284); head and body 134 (128-138); tail 133 (123-148); hind 

 foot 30.2 (29-32). 



Thomasomys cinereus ischyrus subsp. nov. 



Type from Tambo Almirante, near Uchco, Peru. No. 19803 Field 

 Museum of Natural History. Male adult. Collected June 23, 1912, 

 by W. H. Osgood and M. P. Anderson. 



Characters. Similar to Thomasomys cinereus but larger, longer- 

 tailed, and more richly colored; skull with a broader braincase, longer 

 rostrum, and broader interorbital region. Upper parts rich Vandyke 

 brown or burnt umber finely sprinkled with sooty, the blackish slate 

 undercolor scarcely showing through; under parts throughout heavily 

 washed with the same deep fulvous brown but without sooty admixture 

 and with the undercolor showing slightly; ears blackish, the hairs near 

 their inner bases with marked whitish roots; fore and hind feet exten- 

 sively brownish, decidedly more so than in cinereus; tail dull brownish 

 above, scarcely lighter below. 



Measurements. Type: Total length 291; head and body 137; tail 

 154; hind foot 31. Average of six adults : 280 (266-292); 131 (124-137); 

 149 (140-160); 31. Skull of type: Greatest length 33; basilar length 

 25.5; zygomatic width 17.1; least interorbital width 6.4; nasals 13.9 x 

 3.8; interparietal 12.5 x 3.2; palatine foramina 6.7 x 2.3; upper tooth- 

 row 5.1. 



Remarks. Nine of these rats were taken in the forest at Tambo 

 Ventija and four others somewhat farther east and at less elevation at 

 Tambo Almirante. Owing to their greater size in comparison with 

 T. cinereus, they were at first thought to represent T. kalino-wskii. But 

 comparison with the type of that species kindly made by Mr. Thomas 

 shows our specimens to be smaller with smaller narrower teeth and a 

 broader interorbital region. Although well distinguished from cinereus, 

 the new form shows such variation that it can scarcely be regarded as 

 more than a subspecies. 



An interesting character of this species, shown in less degree by 

 certain others of the same and related genera, is the area of white-rooted 

 hairs about the inner bases of the ears. These hairs are distinctly 

 four-colored, the bases being nearly pure white followed broadly by 

 blackish slate, then narrowly by fulvous brown, and apically by blackish. 



