On the Psammomys of the Nile Delta. 91 



of the forearms are fulvous to the elbows. Hind limbs simi- 

 larly bluish grey to the ankles, the grey sharply defined at 

 the hips and quite without the yellowish suffusion which in 

 S. sciurea renders the thighs not markedly different from the 

 sides of the body. Under surface and inner side of limbs 

 whitish, clearer, less yellow-suffused, and more sharply defined 

 than in sciurea. Tail as usual, its underside whitish. 



Dimensions of the type (measured in skin) : — 



Head and body 350 mm. ; tail 41 ; hind foot 83. 



Skull: greatest length 65; basal length 40; zygomatic 

 breadth 42 ; breadth of brain-case 36 ; combined length of 

 upper premolars and molars 13*2. 



Hob. Humayta, Middle Rio Madeira, about 63° W., 

 7° 30' S. 



Type. Adult male. B.M. no. 8. 5. 9. 6. Original num- 

 ber 36. Collected 17th August, 1906, by W. Hoffmanns. 

 Five specimens, adult and young. 



This distinct species is readily recognizable by the marked 

 contrast of its bluish-grey crown, arms, and legs with the 

 yellowish dorsal colour, and especially by the non-extension 

 of the fulvous of the hands above the wrists, this colour 

 extending over the whole of the forearms in S. sciurea. 



S. boliviensis, found on the extreme upper waters of the 

 same river-system, is like S. sciurea in these respects, its 

 special character being its black crown. 



XI. — The Psammomys of the Alluvial Soil of the Nile Delta. 

 By Oldfield Thomas. 



The dark fertile soil of the Lower Nile and its delta con- 

 trasting so markedly with that of the deserts on each side of 

 it, we might expect that certain of the local animals would 

 be moditied in colour to suit it. There is little doubt 

 that this is the cause of the dark colour of the Cairo spiny 

 mouse (Acomys cahirinus) , slaty-grey all over when other 

 members of the genus are more or less reddish or yellowish 

 above and white below, and I now find the same tiling occurs 

 in Psammomys. 



The genus ranges from Algeria and Tunis to Palestine, 

 and contains four or five species distinguished from each 

 other mainly by size and the development of their bullae. 

 All are of a sandy desert colour, including the Egyptian 

 Fs. obesus, of which the type locality is Alexandria, just on 



