RODENTS OF LIBYA 129 



Wassif (1956), in reviewing the dipodils of Egypt, recognized that 

 gerbils representing G. amoenus and G. dasyurus were not of the same 

 species and reinstated the former as a full species with a range con- 

 fined to Egypt west of the Nile. He predicted that specimens from 

 Tripolitania and other localities in Libya also probably represented 

 a variety of G. amoenus. The present author is in agreement with 

 Wassif in considering G. amoenus as a full species, and G. dasyurus 

 is no longer considered as a part of the Libyan mammalian fauna. 



Specimens from the Fezzan are slightly larger in size of body, and 

 their skulls have slightly larger and more inflated auditory bullae 

 than those from Tripolitania and Cyrenaica. Within the Fezzan, the 

 various populations are remarkably similar in cranial and external 

 characters. Specimens from El Gatrun are slightly larger than topo- 

 typical specimens from near Sebha, and a large series from Ghat 

 and El Barcat are correspondingly smaller. To the north in Tripoli- 

 tania, specimens from Zliten and Socna are comparable in size to 

 typical G. a. vivax but have somewhat smaller auditory bullae. 

 Specimens from farther east in Cyrenaica and nearer the type locality 

 of G. a. amoenus are appreciably smaller in size and possess the 

 smallest auditory bullae of any representatives of this subspecies in 

 Libya. This diminution in bullar size in these easternmost populations 

 of gerbils suggests intergradation with G. a. amoenus. A gradient, 

 extending from west to east and showing progressive decrease in size 

 and degree of inflation of the auditory bullae, is apparent in popula- 

 tions of this gerbil in Libya and Egypt. Gerbils with small auditory 

 bullae from the Nile Delta thus represent the easternmost limits of 

 expression of this character, and those with larger auditory bullae 

 from the Fezzan are near the westernmost limits of this character 

 gradient. It appears that the subspecies G. a. amoenus and G. a. 

 vivax actually represent the two extremes in this clinal gradient. 

 It is not uncommon for populations at each end of a cline to develop 

 dissimilarities of sufficient magnitude to warrant designation as 

 distinct subspecies, especially when the clinal character extends over 

 such a wide geographic area. 



While recognizing that the foregoing variation and clinal pattern 

 exists within and between populations of this gerbil in Libya, and 

 even though the easternmost populations show some characters 

 typical of G. a. amoenus, I prefer to assign all of the specimens from 

 Libya to G. a. vivax. 



Four specimens from Biskra and a single specimen from Beni 

 Abbes, Algeria, are within the geographic range ascribed to Gerbillus 

 garamantis (Lataste). In cranial characters, these specimens are 

 strikingly similar to those of G. a. vivax from western Tripolitania 

 and the Fezzan. In cranial measurements, however, gerbils from Libya, 



