RODENTS OF LIBYA 113 



Measurements. Averages and extremes of 31 adult males and 18 

 adult females from the type locality, with the measurements of the 

 type in brackets, are, respectively: Total length 214.4 (202-220), 

 208.1 (200-220), [210]; length of tail 122.5 (117-129), 120.3 (113-128), 

 [122]; length of hind foot 29.4 (28-31), 28.6 (27-30), [29]; length of 

 ear 13.9 (13-14), 13.3 (13-14), [14]; occipitonasal length of skull 

 28.6 (27-29.9), 28.1 (27.3-29.5), [28.5]; length of auditory bulla 10.4 

 (9.8-11), 10.3 (9.7-10.9), [10.5]; crown length of upper molariform 

 toothrow 3.6 (3.4-3.9), 3.6 (3.4-3.9), [3.7]; greatest breadth across 

 zygomatic arches 15.5 (15-16.4), 15.1 (14.7-15.4), [15.7]; least inter- 

 orbital breadth 5.9 (5.4-6.4), 5.7 (5.3-6.2), [5.7]; breadth of rostrum 

 at level of antorbital foramina 3 (2.7-3.2), 3.1 (2.9-3.2), [3]; greatest 

 length of nasals 10.6 (10.4-11.6), 10.5 (10-11.3), [10.6]. 



Diagnosis. Upperparts uniformly Cinnamon-Buff becoming inter- 

 spersed with white hairs on sides and pectoral areas; circumorbital 

 region, rostral area, postauricular areas, and entire underparts white; 

 fore and hind feet Light Buff dorsally, sparsely haired ventrally, and 

 each bearing five digits with claws; pinna of ear Warm Buff, finely 

 haired and with thin row of buffy hairs along anterior margin ; vibrissae 

 short and usually white, but with occasional darker hairs present; tail 

 indistinctly bicolored Light Buff ventrally with narrow dorsal line of 

 Light Ochraceous-Buff terminating in a distinct pencil, Avellaneous 

 dorsally and Light Buff ventrally. Skull: Medium in size; moderately 

 robust; auditory bullae moderately inflated; zygomata heavy; basi- 

 occipital constricted anteriorly and forming distinct foramina near 

 anteromedial margins of auditory bullae; external pterygoid fossae 

 forming distinct depressions dorsal to posteriorly flaring pterygoid 

 hamulae; braincase moderately vaulted. 



Comparisons. From topotypes of Gerbillus gerbillus discolor from 

 Ghat, Fezzan Province, Gerbillus gerbillus psammophilous differs in 

 having narrower auditory bullae, more anteriorly constricted basi- 

 occipitals, larger foramina between basioccipital and auditory bulla, 

 more arched braincase, less divergent pterygoid hamulae, greater 

 occipitonasal length, greater interorbital breadth, and slightly larger 

 hind feet. In color, G. g. psammophilous is much paler and less streaked 

 dorsally and has a less prominent subauricular patch and a lighter 

 pencil. 



Gerbillus gerbillus psammophilous differs from topotypical specimens 

 of Gerbillus gerbillus gerbillus in having heavier zygomata, more 

 anteriorly constricted basioccipitals, more distinct foramina between 

 the basioccipitals and the auditory bullae, smaller, more slitlike 

 posterior palatine canals, shorter overall length, slightly larger 

 occipitonasal length, greater breadth across zygomatic arches, longer 



