484 071 new African Epimys «7iJ Jaculus. 



Skull : greatest length (In middle line) 31 ; condylo- 

 incisive length 28; back of bulla to front of incisors 32*7 ; 

 zygomatic breadth 21 ; interorbital breadth 12'3; tympanic 

 breadth 23 ; diameter of bulla from antero-inferior to postero- 

 superior convexity 14*1 ; upper molar series 5. 



Hah. Trarza Country, S.W. Mauritania. 



Ti/pe. Adult female, skinned from preserving fluid. B.M. 

 DO. 13. 3. 7. 4. Collected by M. Audan. 



This is a very great extension of the range of tiie Dipodidse*, 

 as the Central Algerian Sahara, over 1200 uules off, is the 

 nearest place from which any Jerboa has hitherto been 

 recorded. 



An examination of the Jerboas of this group, which extends 

 from Senegambia to Somali, shows that they should all be 

 looked upon as a single species, with several subspecies, 

 between which the ditferences are size and general tone of 

 colour. At the three extremities of the wide area referred 

 to — Senegambia, Lower Egypt, and Somaliland — the size 

 is decidedly less than in Algeria and the Soudan, as may be 

 gathered from the following series of skull-measurements. 

 The single dimension taken is from the front of the incisors 

 to the back of the buUje : — 



Trarza : 32'7 mm. 



Biskra : 34-5, 34-5, 35-2, 35-4. 



Clentral Algerian Sahara: 35. 



Egyptian Soudan : 35-2, 35'6, 36*3. 



C;airo, Lower Egypt: 323, 32-7, 32-7, 33-5, 33-6. 



Somali : 32*5. 



It will be seen that the nearness together of these dimen- 

 sions, and the geographical situation of the smaller forms at 

 the most distant points round the larger, indicate the advisa- 

 bility of treating the whole as a single species. For to split 

 them into two by size would leave the smaller species a 

 conglomerate of three geographically isolated forms, between 

 which in turn there are no characters to justify specific 

 separation. 



The five subspecies, however, may be provisionally indicated 

 as follows: — 



J.jaculus deserti, Loclie. — Larger, paler. Algeria &c., down to Lake 

 Chad. 



* The separation from each other of Dipus and Jaculus as distinct 

 genera {cf. Ann. & jNkg. Nat. Hist. (8) ii. p. 308, 1908) enables us ta 

 return to the well-known name Dipodidae for the family, instead of the 

 comparatively uufamihar Jaculidse. 



