224 U.S. NATIONAL MUSEUM BULLETIN 2 75 



Arabia) ; Dipus schluteri Nehring, 1901 (type locality: Jaffa, Palestine); 

 and Dipus loftusi Blanford, 1875 (type locality: Mohumrah, Iraq) 

 were referred to Jaculus jaculus by Ellerman and Morrison-Scott 

 (1951, p. 539). I have, however, found that these forms definitely have 

 characters which ally them to the "deserti" type and consider them as 

 subspecies of J. deserti rather than J. jaculus. Henceforth, these forms 

 should be known as Jaculus deserti vocator Thomas, Jaculus deserti 

 schluteri (Nehring), and Jaculus deserti loftusi (Blanford). 



Although intergradation is not demonstrable between populations of 

 Jaculus deserti favillus and Jaculus deserti juscipes in Libya, the ranges 

 of these two subspecies are not separated by physical barriers. In the 

 future, when more adequate series become available, this intergrada- 

 tion will probably become apparent, and clinal gradients will be 

 demonstrable within these two widely distributed populations. Farther 

 east, however, the Nile River appears to serve as an effective barrier 

 for the exchange of genes between J. d. javillus and Jaculus deserti 

 schluteri. 



Jaculus deserti, in the dark color of dorsum and soles of hind feet, 

 resembles Jaculus blanfordi (Murray), whose range lies far to the east 

 and north. This similarity in color is probably the result of conver- 

 gence or a response to a similar color of substrate. Vast areas of gray 

 and brown hamadas are of common occurrence in the ranges of both of 

 these jerboas. Morphologically, J. blanfordi is more closely related to 

 the larger Egyptian jerboa (J. orientalis). 



Ecological observations. Four distinct populations comprise 

 this species in Libya. Jaculus deserti favillus is apparently confined to 

 the more humid Mediterranean coast and adjacent areas of low 

 elevation. Jaculus deserti vastus, J. d. rarus and J. d. fuscipes prefer 

 the more arid deserts of the interior. In general, this species of jerboa 

 is more confined to the "hamadas" or great "pebble deserts" of the 

 Libyan hinterland. In the interior hamadas, vegetation may be entirely 

 wanting or confined to narrow strips along the margins of wadis, the 

 brinks of escarpments, or the fringes of inland "play as." The larger 

 wadis sometimes support stands of acacia of appreciable size, but these 

 are of rare and local occurrence. 



Near the coastal plain at Marble Arch, J. jaculus and J. deserti occur 

 together. In other coastal areas the large Egyptian jerboa (J. orientalis) 

 also occurs sympatrically with these smaller species. 



Jaculus deserti favillus Setarer 



Jaculus jaculus favillus Sctzer, Proc. Biol. Soc. Washington, vol. 68, p. 184, Dec. 31, 

 1955 (Bir Bosslanga; Salum, Western Desert Governorate, Egypt). 



Specimens examined. Two, from Cyrenaica: 10 km SW Fort 

 Capuzzo, 1; from Tripolitania: 15 km WNW Marble Arch, 1. 



