RODENTS OF LIBYA 73 



bushlike growth. The areas of tamarix, sedges, and grasses were 

 trapped intensively, but yields were quite poor. 



This portion of the coastal plain, with its lush and profuse vege- 

 tative cover, is not typical of most of the Cyrenaican coastal plain, 

 and probably at these lower elevations voles are of very sporadic and 

 local occurrence. The range of M. mustersi, in Libya, therefore prob- 

 ably is largely confined to the higher and more typically montane 

 areas of the Cyrenaican Plateau and the Gebel Achdar, which provide 

 more abundant and continuous habitat. 



The occurrence of voles in Cyrenaica poses some very interesting 

 zoogeographic problems, particularly since they are not known from 

 coastal Egypt, the only conceivable dispersal route. It is possible that 

 the population of voles in Cyrenaica are relicts from the period when 

 the more boreal climates of the Pleistocene prevailed over North 

 Africa. The Cyrenaican Plateau by virtue of its higher elevation has 

 retained at least a vestige of these boreal elements, whereas the 

 remainder of coastal Africa has become much drier and more sparsely 

 vegetated and no lons-er contains habitats suitable for voles. 



Subfamily Gerbillinae 



Genus Gerbillus Desmarest 



Lataste (1881, p. 506) divided the genus Gerbillus into two genera, 

 Gerbillus and Dipodillus Lataste, and separated the latter from 

 Gerbillus by the number of plantar pads, the pattern of infolding of 

 enamel on the surfaces of the teeth, and by characteristics of the 

 auditory bullae. According to Lataste, typical members of Gerbillus 

 had one carpal pad and no plantar pads, while representatives of 

 Dipodillus had five carpal and six plantar pads. Lataste used the 

 character of naked feet to separate two species, Gerbillus garamautis 

 Lataste and Gerbillus hirtipes Lataste. Heptner (1937) and Ellerman 

 (1941) suppressed Dipodillus as a full genus. The latter author stated 

 that members of the two genera could not be distinguished by cranial 

 characters and that there was a lack of constancy in the characters 

 used by Lataste to distinguish between the two genera. Later, Wassif 

 (1956) and Setzer (1957) regarded Dipodillus as a subgenus of the 

 older prevailing Gerbillus and used the presence or absence of hair on 

 the hind feet to assign their specimens to the two subgenera. The 

 present author uses this same character to separate the subgenera 

 Dipodillus and Gerbillus, each represented in Libya by four species, 



285 134 O — 68 6 



