236 U.S. NATIONAL MUSEUM BULLETIN 2 75 



of Hun, Socna, and Uaddan provide favorable habitat for jerboas and 

 accordingly allow for genetic exchange between coastal populations 

 and those in the interior. 



In Fezzanese populations of jerboas, genetic uniformity has been 

 maintained owing to the continuity of suitable habitat and conesquent 

 free genetic interchange. Numerous dry watercourses such as the Wadi 

 es Sciati, north and west of Sebha, the Wadi Tenezoft, north of Ghat, 

 and the broad hamadas Unking together the oases of Tesaua, Murzuch, 

 Traghen, Umm el Araneb, Meseguin, Zuila, and Tmessa provide suit- 

 able habitat and insure the maintenance of genetic integrity within and 

 between populations of jerboas in these far-reaching areas. These 

 hamadas and wadis allow jerboas to circumvent the desolate "ramleh" 

 or sandy areas. El Gatrun, however, unlike the aforementioned oases, 

 is effectively isolated by the great sandy areas of the Idehan Murzuch, 

 and three specimens from here show slight differences from populations 

 elsewhere in the Fezzan. Until such time as adequate series become 

 available, I prefer to include jerboas from El Gatrun within the sub- 

 species J. j. arenaceous. 



In the Fezzan, jerboas were obtained from a wide variety of habitats, 

 ranging from practically barren hamadas to the bleak margins of sand 

 seas. In these habitats, plants occur sparingly and are represented by 

 relatively few species, one kind usually being dominant. In most 

 instances, jerboas were not found in the oases proper but in the more 

 open, outlying areas. 



The name arenaceous, meaning of sand or sandy, refers to the 

 sandy color of the pelage of these jerboas. 



Jaculus jaculus collinsi, new subspecies 



Holotype. Adult male, skin and skull, USNM 325797, from 

 Tazerbo Oasis, Cyrenaica Province, Libya; obtained Apr. 15, 1962, 

 by G. L. Kanck, original no. 2039. 



Specimens examined. Twenty, from Cyrenaica: Gialo Oasis, 

 5; Bir el Harasc, 1 ; Bir bu Zarregh, 1 ; Tazerbo Oasis, 11 ; El Gezira, 2. 



Measurements. The averages and extremes of five males and six 

 females from the type locality, with the measurements of the type in 

 brackets, are, respectively: Total length 292 (282-307), 294.2 (275- 

 313), [293]; length of tail 182.2 (175-192), 183.3 (166-197), [182]; 

 length of hind foot 61.6 (61-63), 61 (58-63), [62]; length of ear from 

 notch 22.2 (21-23), 21.7 (21-23), [23]; greatest length of skull 33.6 

 (32.5-34.5), 33.3 (32.3-34.3), [34.4]; condyloincisive length of skull 

 29.9 (28.6-30.9), 29.6 (28.7-34.3), [30.7]; crown length of upper 

 molariform toothrow 5.2 (5-5.3), 5.2 (4.9-5.4), [5.3]; greatest breadth 

 across zygomatic processes 22.2 (21.6-23.4), 21.8 (21.4-22.9), [21.7]; 

 least interorbital breadth 12.2 (11.8-12.3), 12 (11.5-12.6), [12]; length 



