10 ME. OLDFIELD THOMAS OX [May 6, 



As hown elsewhere', the species of Psamonomys, apart from 

 Ps. elegmis, which I do not know, and the much smaller Ps. rou- 

 dairei, fall readily into four distinguishable forms respectively 

 inhabiting Algeria, Tripoli, Lower Egypt, and Palestine. They 

 are distinguished mainly by size and the relative development 

 of their buUfe, their external appearance being all very much the 

 same. 



13. PSAMMOMYS ROUDAIREI Lat. 



14.$. Bonjem. 20 April, 1901. 

 117.2. W. Wagis. 7 July, 1901. 



I have always considered M. Lataste was unnecessarily hasty in 

 withdrawing his name Psammomys roudairei, for thei'e are clearly 

 two species — a larger darker, and a smaller paler one — living 

 together in Algeria and Tripoli ; and, although undoubtedly 

 immature, his two type specimens (of which the British Museum 

 possesses one) evidently belong to the smaller form. The name 

 itself would have stood in any case, for, as has already been seen, 

 the large western Psammomys is different from Ps. obesus, and 

 has not hitherto had a tenable name applied to it. 



The second specimen above recorded is only doubtfully placed 

 here, as it is immature, and members of this group are almost 

 impossible of satisfactory determination unless fully adult. 



14. MUS MUSCULUS ORIEXTALIS Or. 



]. Tarhina. 5 Api^il, 1901. 



15. ACOMYS VIATOR, sp. n. 



90. 2 • "Wadi Sultan, near Sokna. 18/6/1. 



Size fairly large. Spines of back about 11 mm. long, by barely 

 half a millimetre broad. General colour above pale slaty grey 

 anteriorly, changing to dull pale rufous posteriorly. Individually 

 the dorsal spines are pale grey (near smoke-grey of Ridgway), 

 with their extreme points dark brown, and Mdth a narrow pale 

 rufous subterminal band ; under surface pure white throughout. 

 Head and shoulders plain grey, the spines narrower and grey 

 throughout, without darkened points. Ears rather small, pale 

 greyish, a white spot below their outer base. Hands and feet 

 white. Tail of medium length, greyish brown above, white below. 



Skull smaller than in A. dimidiatus, the brain-case of medium 

 size and its ridges not conspicuously heavy or broadened. Palatal 

 foramina to the posterior thii'd of in^. Opening of posterior nares 

 2*3 mm. behind back of m^. Bullae smaller than in A. dimidiatus, 

 their antero-external-postero- internal breadth 4"2 mm. 



Dimensions of the type : — 



Head and body 110"mm. ; tail 107 ; hind foot 19-5 ; ear 19. 



Skull — greatest length 29; basilar length 21-5; zygomatic 

 bi^eadth 14; nasals, length 11 ; interorbital breadth 4*6; breadth 



1 Ann. Mag. X. II. (7) ix. r- S^S (1902). 



