114 U.S. NATIONAL MUSEUM BULLETIN 275 



nasals, and rostra less decurved distally. These gerbils are similar to 

 those of the nominate subspecies in dorsal color but appear slightly- 

 paler owing to a greater suffusion of whitish hairs on sides, more 

 white around the eyes and rostrum, less prominent subauricular 

 patches, and a paler pencil. 



Gerbils representing the nominate subspecies from the vicinity of 

 Giarabub, Cyrenaica Province, resemble those referable to G. g. 

 psammophilous but have larger, more massive skulls, larger, more 

 inflated auditory bullae, and larger anterior palatine foramina. In 

 color, they are almost indistinguishable from topotypes of G. g. 

 psammophilous . 



Gerbillus gerbillus psammophilous can be readily distinguished from 

 topotypical specimens of Gerbillus gerbillus andersoni by much paler, 

 more orangish dorsal color, shorter anterior palatine foramina, less 

 vaulted braincase, less ventrally inflated auditory bullae, shorter and 

 smaller molariform toothrow, more prominent supraorbital bead, less 

 robust zygomata, and smaller size of all cranial measurements. 



From topotypes of Gerbillus gerbillus asyutensis from the Wadi 

 Asyuti, Egypt, G. g. psammophilous differs in having markedly darker, 

 less variegated dorsal pelage, shorter posterior palatine canals, wider 

 basioccipitals, and larger size of all cranial measurements. 



Compared with two specimens, 321821 and 321822, representing 

 Gerbillus gerbillus latastei from 40 kilometers north of Sinauen, 

 Tripolitania Province, G. g. psammophilous has slightly smaller and 

 more ventrally inflated auditory bullae; smaller molariform teeth; 

 heavier zygomata ; shorter occipitonasal length ; shorter tail ; markedly 

 paler, more subdued dorsal color with less suffusion of brownish 

 hairs; a less distinctly bicolored tail; and vibrissae with fewer dark 

 hairs. 



Paratypes of G. g. psammophilous can be distinguished from the type 

 and paratypes of Gerbillus gerbillus aeruginosus from El Giof, Cufra 

 Oasis, by their paler dorsal color and markedly larger size of all 

 cranial measurements, being similar in length of auditory bulla, crown 

 length of upper molariform toothrow, and least interorbital breadth. 

 G. g. psammophilous also has narrower posterior palatine canals, 

 heavier zygomata, more ventrally inflated auditory bullae, less domed 

 skull, and less distally decurved rostrum. 



Remarks. Members of this subspecies show significant intergrada- 

 tion with other subspecies whose major ranges are far removed 

 geographically. Gerbils from Giarabub and Bahr el Tubat, in some 

 characters, suggest intergradation between G. g. psammophilous and 

 the nominate subspecies. In color, gerbils from Tazerbo Oasis, Bir el 

 Harasc, and Bir bu Zarregh show evidences of gene exchange with 

 G. g. aeruginosus to the south. Specimens from near Hun, Socna, and 



