174 U.S. NATIONAL MUSEUM BULLETIN 275 



length of upper molariform toothrow 5.1, 5.1, [5.4]; least interorbital 

 breadth 7.5, 6.4, [7.4]; length of nasals 14.8, 14.5, [15]; breadth of 

 rostrum at level of antorbital foramina 4, 3.6, [3.6]; greatest breadth 

 across zygomatic arches 20.6, 20, [20.5]. 



Diagnosis. Upperparts subdued in color varying in tones of 

 Ochraceous-Buff, Light Ochraceous-Buff, Warm Buff and Pinkish Buff; 

 all parts faintly washed with gray; postauricular patches distinct, 

 almost pure white; region around eyes light gray strongly suffused 

 with black; cheeks and circumoral areas white; eye ring black; vi- 

 brissae long, formed of about equal numbers of black and white 

 hairs; pinna of ear sparsely haired, particularly on medial aspect and 

 with distinct row of buffy hairs along anterior margin; fore feet 

 naked ventrally, buffy-white dorsally and bearing five digits with dark- 

 colored claws; hind feet heavily haired ventrally, except for a promi- 

 nent hairless area confined to proximal half of plantar surface, white 

 dorsally and also bearing five digits with claws; tail relatively long, 

 unicolorous, slightly paler than that of the dorsum, with prominent 

 black pencil occupying distal one-fourth of dorsal surface and ex- 

 tending a short distance along ventral surface. Skull: Relatively 

 large and robust; zygomata heavy and coarse; anterior palatine fora- 

 mina narrow and slitlike; auditory bullae large, markedly inflated 

 both ventrally and laterally, and adnate to squamous portion of 

 temporal bone; suprameatal triangle large and completely enclosed 

 by enveloping processes of the supraoccipital and temporal bone. 



Comparisons. This new subspecies can be distinguished from both 

 Meriones caudatus caudatus of the Tripolitanian deserts and Meriones 

 caudatus confalonierii of the Tripolitanian and Cyrenaican coastal 

 plains by its larger body size, being larger in all cranial measurements 

 except breadth of rostrum, alveolar length of upper molariform 

 toothrow, and zygomatic breadth. In external measurements, Meriones 

 caudatus luridus is larger in greatest length and length of tail but of 

 comparable length in the length of hind foot and ear. 



Although animals belonging to M. c. luridus are of large size, they 

 still differ strikingly from M. c. amplus in having smaller and more 

 gracile crania, particularly the zygomata, and smaller external 

 measurements. 



In its markedly paler, more yellowish dorsal color, particularly 

 that of the tail, and in the less conspicuous pencil, this subspecies 

 differs strikingly from all other subspecies of Meriones caudatus. 



Remarks. Toschi (1951 and 1954) assigned specimens from the 

 vicinity of Giarabub to Meriones libycus libycus and Meriones libycus 

 caudatus. Sympatry of two subspecies of the same species is not in 

 accordance with modern systematic and evolutionary concepts. In 

 the present work, however, M. libycus and M. caudatus are considered 



