228 U.S. NATIONAL MUSEUM BULLETIN 275 



J. d. fuscipes is slightly darker dorsally with a more prominent ad- 

 mixture of black hairs on lateral margins of rump and darker hairs 

 on soles of hind feet. Cranially, these two subspecies are quite similar, 

 but J. d. fuscipes can be distinguished by its longer molariform tooth- 

 row, slightly more vaulted skull, more robust zygomata, and larger 

 and more distinct foramina on the angular process. 



Jaculus deserti fuscipes differs from Jaculus deserti vastus in markedly 

 smaller size of external and cranial measurements except length of ear, 

 condyloincisive length of skull, length of molariform toothrow, and 

 greatest breadth of braincase. Jaculus deserti vastus is paler and more 

 uniform in color of dorsum with less admixture of dark hairs, lacking 

 blackish hairs on lateral margins of the rump, and is more buffy 

 ventrally. 



Remarks. This subspecies of jerboa can be distinguished from all 

 others in Tripoli tarda by its markedly darker dorsal color, darker 

 hairs on the sole of the hind foot, more compact skull, the presence 

 of two distinct foramina in the angular process, larger and more 

 greatly inflated auditory bullae, and proportionately wider upper 

 incisors. 



The range of Jaculus deserti fuscipes includes the extensive hamadas 

 of central and northern Tripolitania. Throughout these "pebble 

 deserts," vegetation occurs sporadically in localized concentrations 

 along the margins of dry watercourses and other low-lying areas. 

 These jerboas probably have a much wider distribution in Libya than 

 is currently supposed. 



The above specimens were all obtained from these interior hamadas. 

 The type locality, although near the Mediterranean coast, is typical 

 "hamada" desert and has no physical relationship to the nearby 

 coastal plain. Fat-tailed sand rats {Pachyuromys duprasi) also show 

 a decided preference for this rocky, upland type of habitat and were 

 obtained at Rumia and El Gheddahia along with jerboas. 



The specimens from near Bir Allagh and Rumia are darker dorsally 

 and have a greater suffusion of dark hairs on the soles and metatarsal 

 areas of hind feet than the specimens from the type locality but are 

 definitely referable to this new subspecies. 



The subspecific name fuscipes refers to the dark-colored soles of 

 the hind feet. 



Jaculus deserti rarus, new subspecies 



Holotype. Adult male, skin and skull, USNM 319781, from Ain 

 Zueia, Gebel Uweinat, Cyrenaica Province, Libya; obtained Mar. 26, 

 1961, by H. W. Setzer, original no. 2987. 



Specimen examined. The type only. 



Measurements. The type specimen measures: Total length 296; 

 length of tail 184; length of hind foot 61; length of ear 24; greatest 



