Dipodillus and PsamniDinyr^. 363 



Dimensions of tlie type (measured in tlie tle.sli) ; — 



Head and body 82 millim. ; tail UO ; hind foot 20; 

 car lO-.G. 



Skull: greatest length 2)'j; basilar length 19"o ; zygo- 

 jnatie breadth 14*2; nasals 98 ; interorbital breadtli 4:'6 ; 

 breadth of brain-case 11"8; interparietal 3"5 X 6"7; diastema 7; 

 palatal foramina 4 ; greatest diameter o£ bulla 9 ; length of 

 upper molar series 3'1. 



J lab. Lahej, near Aden. 



Type. Female. B.M. no. 99. 11. 6. 44. Collected 23rd 

 August, 1899, by \V. Dodson. 



This specimen had been supposed to be a young individual 

 of D. pcecilops, to wliich it has an extraordinary resemblance, 

 but an examination of its skull shows that it is fully adult 

 and belongs to a group, that of D. quadriniaculafus and its 

 allies, not previously recorded from east of the lied Sea. 



The Larger Species of Psammomys. 



Aj)art from Psammomys elegans^ Heugl., which I do not 

 know, and the small pale-coloured Ps. Ltoudairei^ Lataste, 

 the species of Psammomys seem to be four, respectively in- 

 habiting Algeria, Tripoli, Egypt, and Palestine. Externally, 

 so far as our material shows, they are all very much alike, 

 but their skulls may be readily distinguished by size and the 

 relative development of their bulUe, as follows : — 



1. Ps. algiricusj sp. n. 



Size large, upper length of skull about 43-45 millim. 

 Bullse medium, their greatest diameter 16 millim. 



2. Psammomys of Tripoli (described in ' Proceedings of the 



Zoological Society,' 1902). 



Size smaller, upper length of skull 41 millim. Bullse 

 small, their greatest diameter 14 1-14*3 millim. 



3. Ps. obesus, Cretschzm. 



Size greater than in the Tripoli species, upper length of 

 skull 43 millim. BuUfe smaller, diameter lo'5 millim. 



4. Ps. terrcB-sancUe^ sp. n. 



Size very large, skull elongate, its upper length over 

 46 millim. Bulke largest in the group, their diameter 

 18 millim. 



It should be premised that a very slight difference in the 

 linear diameter of the buUaj indicates a very considerable 

 difference in their cubic bulk. 



