250 U.S. NATIONAL MUSEUM BULLETIN 275 



ventral margin of coronoid process; angular process reduced and with a 

 single trianguliform foramen on an tero ventral margin; molariform 

 teeth large, lower incisors thin and attenuated. 



Comparisons. Specimens from Gheminez are slightly larger 

 cranially and in external body measurements than specimens from 

 Burg el Arab, Western Desert Governorate, Egypt. In color, animals 

 from Libya are more uniform and less streaked dorsally, have more 

 darkly colored soles of the hind feet and metatarsal areas, have a more 

 prominent buffy patch above the eye, and are less suffused with buff 

 on the sides and pectoral areas. 



Remarks. The above differences are of insufficient magnitude 

 to be of taxonomic significance and probably fall within the range of 

 variation for the species. In view of the wide geographic range of 

 Allactaga tetradactyla, it has undergone comparatively little local 

 differentiation. Setzer (1958) referred to this genetic stability and 

 was also unable to demonstrate significant variation either between 

 or within populations of this kind of jerboa. Apparently, suitable 

 habitat occurs uninterruptedly throughout its range and, as a con- 

 sequence, there has been little interruption of gene flow. When 

 adequate series of A. tetradactyla become available, however, some 

 variation undoubtedly will be demonstrable, and this species will 

 prove to be polytypic. 



Ellerman and Morrison-Scott (1951) did not include Libya within 

 the range of A. tetradactyla. Apparently, they were unaware of the 

 collections reported by Festa (1925) and de Beaux (1932) from Zauia 

 Mechili and El Agheila. The present study contributes but little to 

 the knowledge of the distribution of this kind of jerboa. The few 

 collecting localities in Cyrenaica do suggest a limited occurrence 

 in Libya but probably do not provide an accurate distributional 

 picture. As with most uncommon species, the few collecting sites 

 indicate a fortuitous meeting of collector and animal and do not 

 render an accurate estimate of the population size. 



Ecological observations. The four-toed jerboa inhabits the 

 hamadas of the Mediterranean littoral. These coastal deserts are 

 relatively free of sand and are composed of boulder-strewn plains 

 where vegetation grows sparingly or is frequently wanting. These 

 jerboas apparently dislike habitats of a sandy character and accord- 

 ingly are unknown from the Saharan interior. The collecting locality 

 at Zauia Mechili is still well within the zone of coastal hamadas 

 and has no real relationship to the Sahara proper. 



Setzer (1957) obtained the small series from Gheminez by digging 

 the animals from their burrows but was unable to obtain specimens 

 by trapping. Collecting efforts by the author were to no avail. 



