RODENTS OF LIBYA 135 



zygomatic breadth, shorter nasals, and shorter and less inflated 

 auditory bullae. 



This new subspecies can be readily distinguished from Gerbillus 

 campestris patrizii by its darker, more uniform dorsal coloration and 

 noticeably larger size of body and cranium, being comparable only in 

 length of the auditory bullae and length of upper molariform toothrow. 



Remarks. Members of this subspecies can be distinguished from 

 all others in Libya by their darker, more uniform dorsal color and 

 somewhat longer and less tufted tails. Setzer (1957) assigned specimens 

 from the Cyrenaican Plateau to G. c. dodsoni. His assignment was 

 based solely upon some notes characterizing the type specimen of 

 G. c. dodsoni in the British Museum and upon favorable comparison 

 with the original description of Dipodillus dodsoni as given by Thomas 

 (1902). In the present study, more specimens are available from the 

 Cyrenaican Plateau, and topotypes of dodsoni, in addition to large 

 series from various other localities in Libya, are on hand. Thus, the 

 taxonomic status of these specimens from the Cyrenaican Plateau can 

 be determined more accurately. 



The range of this subspecies is confined to the uplands of the Cyre- 

 naican Plateau and the adjacent littoral areas. Intergradation between 

 G. c. brunnescens and G. c. wassifi of extreme northeastern Cyrenaica 

 and coastal Egypt is apparent in specimens from the coastal areas 

 near Derna and Apollonia. In their pale dorsal color, large cranial 

 size, and wide anterior palatine foramina, they resemble G. c. wassifi, 

 but in the size and degree of inflation of the auditory bullae and in all 

 other cranial characters, they are closer to G. c. brunnescens and are 

 assigned to this subspecies. The vast areas of central Cyrenaica, in- 

 cluding Gialo Oasis and the Gebel el Harug el Asued, and the littoral 

 deserts and coastal plain along the Gulf of Sirte are not represented by 

 specimens and thus create a decided gap in distribution. The two 

 specimens from near Coefia, representing the southernmost record of 

 distribution for G. c. brunnescens, show no evidences of gene exchange 

 with G. c. dodsoni, whose range is farther to the south and west. 



Within populations of this subspecies in Cyrenaica, local variation 

 in dorsal color is apparent. The pattern of this color gradient is too 

 irregular to suggest clinal variation and probably a genetic response 

 to the local character of the substrate. Gerbils from the coastal plain, 

 where the soils are darker, tend to be darker and more uniform in 

 dorsal color than those from the plateau. This dark dorsal color 

 reaches its extreme in specimens from the vicinity of Tocra. 



Ecological observations. These rodents are the most abundant 

 gerbils in the Cyrenaican Plateau and were regularly taken in trap- 

 lines. Other dipodils were collected on the plateau, but they were 

 fewer in number. Members of this subspecies occupy almost all of the 



