RODENTS OF LIBYA 107 



Comparisons. From topotypes of Gerbillus gerbillus gerbillus, the 

 type and paratypes of G. g. discolor differ in having narrower anterior 

 palatine foramina and posterior palatine canals, slightly more 

 inflated auditory bullae, shallower pterygoid fossae, shorter skulls, 

 shorter nasals, greater zygomatic breadth, and more robust skulls. 

 Gerbils from the Fezzan are smaller in overall length and length 

 of tail and hind foot; in color, they are noticeably darker and appear 

 more streaked owing to a greater admixture of brownish hairs on 

 dorsum. 



Two specimens, 321821 and 321822, from 40 kilometers north 

 of Sinauen and a single specimen, 321825, from 5 kilometers east 

 of Derg, Tripolitania Province, are referable to Gerbillus gerbillus 

 latastei and differ from those of G. g. discolor in having wider anterior 

 palatine foramina, more gracile zygomata, more vaulted braincases, 

 and larger external and cranial measurements, being of comparable 

 size only in least interorbital breadth and length of nasals. In color, 

 these specimens from Tripolitania are more uniform in dorsal color, 

 with less suffusion of brownish hairs. 



When the type series of G. g. discolor and Gerbillus gerbillus aeru- 

 ginosa are compared, G. g. discolor differs in having slightly paler, 

 more variegated dorsal color, wider and more inflated auditory bullae, 

 narrower posterior palatine canals, larger cheek teeth, proportion- 

 ately smaller and deeper pterygoid fossae, wider basioccipitals, and 

 markedly larger size of all external and cranial measurements, except 

 length of hind foot and breadth of rostrum at the level of the antorbital 

 foramina. 



For comparison with Gerbillus gerbillus psammophilous, see account 

 of that subspecies. 



Remarks. Gerbils from Edri, near the northern limits of the range 

 of G. g. discolor, are similar cranially to topotypes of G. g. discolor 

 from Ghat, Fezzan. They are intermediate in color, however, between 

 that of a single representative, 321825, of Gerbillus gerbillus latastei 

 from Derg, Tripolitania, and topotypes of G. g. discolor. The color of 

 these specimens from Edri suggests a relationship to G. g. latastei 

 whose range is to the north. Unfortunately, specimens are not avail- 

 able from the Hamada el Hamra and the Hamada de Tinrhert which 

 are located north of Edri and between the ranges of G. g. latastei 

 and G. g. discolor. Although sandy habitats are not widespread in 

 these hamadas, localized sandy areas are present and doubtless 

 support small populations of these rodents. These hamadas, there- 

 fore, provide an avenue through which gene exchange takes place 

 between populations of G. g. latastei to the north and those of G. g. 

 discolor to the south. Gerbils inhabiting these regions may be inter- 

 grades between these two subspecies. 



