152 U.S. NATIONAL MUSEUM BULLETIN 2 75 



species of Gerbillus dasyurus (Wagner). The latter assignment has no 

 morphological or taxonomic justification, as the two forms have 

 nothing in common to suggest conspecificity. Setzer (1958), although 

 recognizing that these gerbils from Egypt and those from Algeria were 

 related, considered the Egyptian specimens to represent a new species, 

 G. kaiseri, distinguished from G. simoni primarily by its significantly 

 longer tail. He did not compare the crania of the two species but in- 

 ferred that those of G. kaiseri would be larger and suspected those of 

 G. simoni to be about the same size as those of G. henleyi. Judging 

 from the single specimen of G. simoni from Guelt es Stel, Algeria, the 

 two species are somewhat comparable in cranial size, but G. simoni 

 appears to be more robust, particularly in having heavier and more 

 massive zygomatic arches. Compared to G. henleyi, both G. kaiseri 

 and G. simoni are markedly larger cranially, have much shorter and 

 more unicolorous tails, proportionately smaller auditory bullae, 

 larger ears, and larger size of body. 



The present series from Cyrenaica and Tripolitania constitutes the 

 first record of occurrence of G. kaiseri in Libya. Gerbils from the 

 Cyrenaican coast differ from topotypes and near topotypes of G. 

 kaiseri from Egypt in their slightly darker dorsal color and shorter 

 tails, but in all other characters the two populations are almost 

 indistinguishable. Specimens from the Gebel Nefusa in Tripolitania, 

 although geographically closer to the type locality of G. simoni in 

 Algeria, possess all characters typical of G. kaiseri and show no evi- 

 dences of interbreeding with G. simoni. It is now clear that G. kaiseri 

 and G. simoni represent two distinct species with separate ranges 

 ascribed to each. The range of the former includes the littoral areas 

 and coastal escarpments of Libya and Egypt, and G. simoni is con- 

 fined to the high plateaus of the Algerian Atlas. 



Within Libya the various discontinuous populations are remarkably 

 uniform in color and cranial characters. Specimens from Derna, how- 

 ever, are slightly darker than those from elsewhere in Cyrenaica, 

 and four specimens from Tripolitania have smoother, more sparsely 

 haired tails than any of the other populations of this gerbil in Libya. 

 Adequate series are still lacking and a more thorough analysis of the 

 differentiation among the various populations will have to be deferred 

 until a later date. It is doubtful that populations distributed over such 

 a wide geographic area represent the same subspecies. 



Ecological observations. In Cyrenaica these gerbils are confined 

 to the relatively narrow coastal plain and adjacent lowlands. Appar- 

 ently they prefer habitats lacking sand. Traplines set throughout 

 coastal dunes failed to take any of these gerbils. Farther west in 

 Tripolitania four specimens were collected from the highest portions 

 of the Gebel Nefusa in the upper reaches of narrow, grassy valleys 



