﻿14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 59 



formly dark underparts and lack of contrast to the color of the 

 dorsal surfaces. 



In making an examination of the specimens from Uganda, two 

 specimens of the group known as Mylomys, by Thomas, were dis- 

 covered. These were taken at the same locality where the present 

 type was secured. Externally they can be recognized by their longer 

 tails and pure white underparts, but these differences only hold 

 good with the fallax group. One of the Angola species, P. campauce, 

 has an equally long tail and similar white underparts to the mem- 

 bers of the Mylomys division. This species also occurs with a 

 member of the P. fallax group, over part, at least, of its range. An 

 examination of the teeth, however, shows it to be a typical Pelomys, 

 with short tubercles and with the third lower molar having in the 

 second lamina only one, the inner cusp, which is enlarged. In 

 Mylomys the cusps of the cheek teeth are higher, and the M 3 

 has besides the inner cusp of the second lamina, a small outer one 

 as well, but it is minute and less developed than in the Desmomys 

 group. The dental characters of Mylomys are slight, and are not 

 accompanied by any marked external characters. Geographically, 

 the two groups are only known to be associated in Uganda, and it 

 is not unlikely that we have here only a single generic type to deal 

 with. 



I am indebted to Mr. Oldfield Thomas for the privilege of 

 describing this new race. 



SACCOSTOMUS ISIOL^, new species 

 Samburr Pouched Rat 



Type from the Isiola River, Northern Guaso Nyiro, British East 

 Africa ; adult female ; number 181803, U. S. Nat. Mus. ; collected by 

 Edmund Heller, July 1, 191 1 ; original number, 1908. 



Characters. — Similar to mearnsi, but differing in longer tail, 

 darker dorsal coloration and small post palatine pits like umbri- 

 venter, from which latter it differs by shorter nasals, wider inter- 

 orbital region and longer tail ; mesopterygoid fossa narrow and more 

 acutely pointed than in any other species. 



Coloration. — Dorsal color drab, the median region black lined; 

 head and sides light drab; ears blackish; feet white; underparts 

 pearl-gray, contrasting little with the sides ; hair basally plumbeous, 

 except on chin and fore throat, where it is white to the roots ; tail 

 bicolor, sepia above, whitish below. 



