2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 66 



very much in color, but is a slightly smaller animal with a longer 

 tail. The ranges of the two forms are separated ty that of A. a. 

 ruhescens, which occupies the eastern side of the Nile system in 

 Uganda, from Ankole to Gondokoro. The Nile appears to be an 

 effective barrier between the ranges of the subspecies ruhescens and 

 centrosus. In I.ado this new form ranges with Arvicanthis tes- 

 ticularis jehclcc Heller, but specimens can readily be separated from 

 skins of that form by their much darker color, above and below 

 yjebelcc has a white belly, sharply marked from the color of the 

 flanks), and by the shorter tail. 



DASYMYS HELUKUS NIGRIDIUS, subsp. nov. 



Type from Naivasha Station, British East Africa, skin and skull 

 of female adult (teeth moderately worn), collected August 20, 1909, 

 by J. Alden Loring. Orig. No. 7054. 



Suhspecific characters. — Differs from Dasymys hclukus helukus 

 and D. h. savannus in larger size and darker color ; skull and teeth 

 larger. Fur long and silky. 



Color of type specimen. — General color of upperparts brownish 

 fuscous, darker on mid-dorsal line where there is considerable purple 

 and green iridescence ; paler and more brownish on sides, where the 

 colors blend into the much lighter grayish buff of the underparts. 

 The upperparts are everywhere speckled with fine lines of golden 

 buff; underfur dark neutral gray. Head and cheeks brownish gray, 

 with considerable of the greenish iridescence around eyes and be- 

 tween ears ; ears dull seal brown. Underparts grayish buff, the hair 

 long; neutral gray, tipped with olive buff. Hands and feet thinly 

 covered with long hairs of brown, darker than in the neighboring- 

 forms. Tail closely annulated ; the numerous hairs of brown above 

 and buff below not covering the scales. 



Skull and teeth. — Skull somewhat larger than in either of the 

 neighboring forms, helukus and savannus, with higher sinciput, 

 heavier rostrum, and greater interorbital breadth. Teeth larger. 



Measurements of type specimen. — Head and body, 176; tail ver- 

 tebrae, 162; hind foot, 36 (dry, without claws, 33.2). Skull: Con- 

 dylobasal length, 38.4; zygomatic breadth, 20.1; length of nasals, 

 13.8; interorbital breadth, 4.7; upper tooth row, alveoli, 8.0; lower 

 tooth row, alveoli, 7.6. 



Specimens examined. — Nineteen from the type locality and one 

 from the Aberdare Mountains at 7,000 feet. 



