226 U.S. NATIONAL MUSEUM BULLETIN 275 



The specimens from Libya, although clearly referable to J. d. 

 favillus, differ from topotypes of the latter in having slightly shorter 

 ears, paler color of dorsum, longer molariform toothrows, greater 

 least interorbital breadth, and the two foramina of the angular 

 process larger, more distinct, and more uniform in size. 



For comparisons with J. d. fuscipes, J. d. rarus, and J. d. vastus, 

 see accounts of those subspecies. 



Remarks. This subspecies was originally assigned to J. jaculus by 

 Setzer (1955) and considered by him to represent an eastward ex- 

 tension of the Libyan fauna into Egypt. The present study indicates, 

 however, that this subspecies has a much wider distribution in Libya 

 and Egypt than was formerly supposed and shows characters allying 

 it with J. deserti rather than to J. jaculus. 



The specimen from Fort Capuzzo was taken alive while making 

 a nighttime check of a trapline which was set in a localized pocket 

 of vegetation in a sandy depression in the otherwise denuded coastal 

 plain. The plants forming these sporadic "pockets" of vegetation 

 were composed of juniperous species and other woody shrubs. 



The habitat at Marble Arch is similar to that of the coastal plain 

 at Fort Capuzzo but with more widespread areas of rocky hamada. 



Jaculus deserti favillus apparently represents a population of 

 jerboas of large size restricted to the more humid environs of the 

 coastal plain and low-lying areas of the Libyan and Egyptian littoral 

 deserts, and it is genetically distinct from those of the Saharan 

 interior. Setzer (1958) suspected that the range of this subspecies 

 was restricted to the humid areas of the Mediterranean coastline. 



Jaculus deserti fuscipes, new subspecies 



Holotype. Adult female, skin and skull, USNM 322761, from 

 7 km S El Gheddahia, Tripolitania Province, Libya; obtained Dec. 3, 

 1961, by G. L. Ranck, original no. 909. 



Specimens examined. Five, from Tripolitania: 20 km E Rumia, 

 1; 7 km S El Gheddahia, 3; 55 km SW Bir Allagh. 1. 



Measurements. Averages and extremes of three females from the 

 type locality, with the measurements of the type in brackets, are, 

 respectively: Total length 287 (285-290), [290]; length of tail 180.7 

 (173-192), [192]; length of hind foot 61.7 (61-62), [62]; length of ear 

 23.7 (23-24), [24]; greatest length of skull 34 (33.7-34.4), [34]; con- 

 dyloincisive length of skull 30.5 (30.2-30.7), [30.2]; crown length of 

 upper molariform toothrow 5.3 (5.3-5.3), [5.3]; greatest breadth 

 across zygomatic processes 22.7 (21.5-23.5), [23.5]; least interorbital 

 breadth 12.4 (12.2-12.6), [12.6]; length of nasals 12.0 (11.7-12.4), [11.8]; 

 breadth of rostrum at level of antorbital foramina 5 (4.6-5.2), [5.2]; 



