138 U.S. NATIONAL MUSEUM BULLETIN 275 



Algeria, to D. dodsoni and included all of Tripolitania and portions 

 of the Fezzan within the range of D. dodsoni. The present work 

 indicates that the range of G. c. dodsoni is confined to western and 

 central Libya and perhaps includes portions of eastern Algeria and 

 Tunisia. 



Gerbils from the Gebel es Soda and the Gebel Nefusa are paler 

 in dorsal color and have larger, more inflated auditory bullae than 

 those from other localities in Tripolitania. Representatives of this 

 subspecies from near Cussabat are darker in dorsal color and have 

 less tufted tails than those of populations to the south. Specimens 

 from near Ghat, Temenhint, and Ubari, in the Fezzan, have markedly 

 more tufted tails (sometimes the pencil occupies one-half the total 

 length of the tail), less streaked dorsal pelage, slightly larger auditory 

 bullae, and are slightly larger in general size than those from Brach 

 farther north. Except for slightly larger auditory bullae in gerbils 

 from the Fezzan, those from Tazerbo Oasis in Cyrenaica and from 

 Brach in the Fezzan, although widely separated geographically, are 

 indistinguishable in color and cranial characteristics. All of the 

 specimens here assigned to G. c. dodsoni possess prominently tufted 

 tails and have large, inflated auditory bullae, which are the most 

 diagnostic characters of this subspecies. 



No specimens of G. campestris are available from the oasis of Gialo, 

 but because this species is widespread to the north and occurs abun- 

 dantly in the remote oases farther to the south in Cyrenaica, probably 

 they occur here also. Gialo is located between the ranges of G. c. 

 brunnescens and G. c. dodsoni, and when specimens of G. campestris 

 become available from Gialo, they may possess characters of both 

 subspecies. 



With the exception of the large series from Brach, only six additional 

 specimens of this subspecies were obtained from the Fezzan. These 

 few specimens do not provide a reliable index to their actual numbers. 

 Suitable habitat is of widespread occurrence throughout the various 

 wadis, serirs, and oases of the Fezzan, and any barriers to dispersal 

 are of local extent. It is probable that these gerbils occur in all the 

 major oases in the Fezzan and also those of southern and central 

 Cyrenaica. This species has not been recorded from the Tibesti 

 Mountains but probably occurs there. 



Evidences of gene exchange with other subspecies are lacking, 

 probably owing to the largely disjunct distribution of this subspecies 

 and also to the lack of specimens from most of the marginal areas; 

 hence, comparisons are not possible. Intergradation with G. c. brun- 

 nescens probably takes place somewhere along the littoral areas of 

 the Gulf of Sirte, and gene exchange with G. c. rozsikae and the 

 nominate subspecies may take place somewhere among populations 



