RODENTS OF LIBYA 167 



completely enclosed by enveloping processes of the temporal and 

 supraoccipital bones. 



Comparisons. From representatives of Meriones caudatus caudatus 

 from 55 kilometers southwest of Bir Allagh, Tripolitania, the type 

 and paratypes of M. c. ampins differ in much larger and more robust 

 crania, particularly the zygomata, larger overall size, and noticeably 

 lighter dorsal pelage with less suffusion of black. Meriones caudatus 

 ampins also has proportionately smaller molariform teeth, and the 

 lateral meatal expansion is less closely adpressed to the squamous 

 portion of the temporal bone. 



Members of this new subspecies can be easily distinguished from 

 those of Meriones caudatus conjalonierii from coastal Tripolitania 

 and Cyrenaica by markedly larger and more robust skulls, larger 

 overall size, and paler dorsal coloration. 



Meriones caudatus ampins can be distinguished from Meriones 

 caudatus Inridus from the vicinity of Giarabub, Cyrenaica, by larger 

 size of skull and external dimensions, more conspicuous pencil, and 

 darker (less yellowish) dorsal color, particularly that of the tail. 



Remarks. In its much larger size, both cranially and in external 

 features, Meriones caudatus ampins is clearly distinct from all other 

 subspecies of Meriones caudatus. In color, it is closest to Meriones 

 caudatus caudatus of the Tripolitanian deserts, although it has much 

 less black on the dorsum. Cranially, this subspecies most nearly 

 resembles Meriones caudatus luridus from northeastern Cyrenaica. 

 The latter is also a form of rather large cranial size, but M. c. amplus 

 is still significantly larger. 



Except for a few specimens representing Meriones crassus from Umm 

 el Abid, Zieghen, and the "Serir" of Murzuch, collected by Edward 

 Dodson of the Whitaker Expedition to Tripoli in 1901, the present 

 series constitutes the first record of occurrence of members of this 

 genus from the Fezzan. 



Because of larger size, M. c. amplus might well be regarded as a 

 distinct species, but because of general resemblance to other sub- 

 species of M. caudatus in color, body form, general external characters 

 and in proportions, shape, and configuration of the skull, probably 

 it represents only an extreme in a clinal gradient. 



This subspecies shows no evidence of gene exchange with Meriones 

 caudatus caudatus to the north. The Gebel es Soda and the barren 

 areas of the Hamada de Tinrhert and Hamada el Hamra apparently 

 restrict interbreeding between populations of these two subspecies. 

 This apparent allopatry has resulted in morphological divergence 

 in the Fezzanese populations, and this subspecies actually may 

 represent an incipient species. 



