128 U.S. NATIONAL MUSEUM BULLETIN 2 75 



From a single specimen of Gerbillus mackilligini (Thomas) from 

 Wadi Kansisrob, Sudan Government Administrative Area, Egypt, 

 specimens of G. a. vivax are noticeably smaller in overall size, more 

 variegated in dorsal color, and have shorter, more particolored and 

 less tufted tails, smaller hind feet, smaller and less inflated auditory 

 bullae, shorter anterior palatine foramina and posterior palatine 

 canals, less expanded braincases, and are smaller in all measurable 

 cranial characters. 



Compared to Gerbillus campestris dodsoni, G. a. vivax is much 

 smaller cranially and in overall size, has a noticeably shorter 

 and less tufted tail, considerably larger and more inflated auditory 

 bullae, and much shorter anterior palatine foramina. 



Remarks. Originally, Thomas (1902, p. 8) described Dipodillus 

 vivax from Sebha, Fezzan Province, Libya, and stated that it was 

 closely related to Dipodillus quadrimaculatus Bodenheimer and 

 Dipodillus amoenus de Winton of the D. quadrimaculatus group of Egypt 

 but differed from both by its decidely larger auditory bullae, narrower 

 basioccipital, and more uniform "ochraceous buffy" color. He thus 

 considered D. vivax as distinct from D. amoenus and regarded D. vivax 

 as the Tripolitanian representative of the quadrimaculatus group of 

 Egypt. 



Later, Ellerman and Morrison-Scott (1951), Toschi (1954), and 

 Setzer (1957) regarded D. amoenus and D. vivax as conspecific but 

 included them as subspecies of Gerbillus dasyurus (Wagner), whose 

 range had previously been limited to Sinai and areas to the north 

 and east. The above workers had only a few specimens, and their 

 assignments probably were based largely upon geographic grounds. 

 In the present study, large series of topotypical G. dasyurus from 

 Sinai and G. amoenus from Egypt are available; the two groups were 

 more critically compared, and the following differences are noted: 

 Specimens of G. dasyurus are significantly larger in all cranial and 

 external measurements, have longer, denser, and more lustrous fur, 

 appear more variegated dorsally, and have longer and noticeably 

 more tufted tails, more inflated braincases, relatively narrower rostra, 

 longer and more slitlike anterior palatine foramina and wider basioc- 

 cipitals. It is evident that G. amoenus is a species distinct from G. 

 dasyurus and that the latter is confined, as was previously thought, 

 to areas east of the Nile River. 



Toschi (1954) assigned specimens from Gheminez to G. dasyurus 

 amoenus (=G. amoenus amoenus) and those from other widely scattered 

 localities, including Cufra Oasis, to G. dasyurus vivax ( = G. a. vivax). 

 Setzer (1957), with reservations, included the few specimens available 

 to him within the subspecies G. a. vivax and did not recognize the 

 nominate subspecies as occurring in Libya. 



