104 U.S. NATIONAL MUSEUM BULLETIN 275 



of Giza, Western Desert Governorate, Egypt, Gerbillus gerbillus 

 aeruginosus differs in smaller size, shorter tail and hind feet, smaller 

 cranial measurements, heavier zygomata, slightly larger and more 

 divergent upper molariform toothrows, more laterally expanded 

 pterygoid fossae, slightly larger lachrymals, and narrower basioc- 

 cipitals. In color, G. g. aeruginosus is darker dorsally, the tail is less 

 distinctly bicolored, and the buffy dorsal color extends farther ventrally 

 and laterally. In general, the range of color in G. g. aeruginosus is 

 much greater than in the nominate subspecies. 



Compared with topotypes of Gerbillus gerbillus asyutensis Setzer 

 from the beginning of the Wadi el Asyuti, 13 miles southeast of 

 Asyuti, Eastern Desert Governorate, Egypt, G. g. aeruginosus differs 

 in darker, more uniform and less variegated dorsal pelage, larger 

 posterior palatine canals, larger molariform teeth, narrower basioc- 

 cipitals, less ventral inflation of auditory bullae, larger anterior 

 palatine foramina, and larger size of all external and cranial measure- 

 ments. 



Specimens of Gerbillus gerbillus sudanensis Setzer from the Anglo- 

 Egyptian Sudan can be readily distinguished from G. g. aeruginosus 

 by their paler dorsal color and markedly smaller external and cranial 

 measurements. 



From measurements of Gerbillus gerbillus agag Thomas from El 

 Fasher, Anglo-Egyptian Sudan, G. g. aeruginosus differs in shorter 

 tail, slightly larger body size, shorter skull, shorter molariform 

 toothrow, shorter nasals, and greater breadth across the zygomatic 

 arches. Only three subadult specimens of G. g. agag are available for 

 study and, in color, these closely approximate G. g. aeruginosus. 



Gerbillus gerbillus aeruginosus differs markedly from gerbils repre- 

 senting Gerbillus gerbillus andersoni de Winton from the vicinity of 

 Alexandria, Egypt. The latter are noticeably larger in all cranial 

 characters, particularly in the size of the anterior palatine foramina, 

 posterior palatine canals, molariform teeth, and the auditory bullae. 

 The skull is more domed and narrower in G. g. andersoni, and the 

 dorsum and ears are conspicuously darker. 



For comparisons with Gerbillus gerbillus discolor and Gerbillus ger- 

 billus psammophilous , see accounts of those subspecies. 



Remarks. In body and cranial size, animals referable to Gerbillus 

 gerbillus aeruginosus are among the smallest of the species of Gerbillus 

 gerbillus in Libya. This trend toward small body and cranial size 

 is apparent in all populations of this species to the east and south. 

 G. g. asyutensis from central Egypt, G. g. sudanensis, and G. g. agag 

 from the Sudan, and gerbils representing G. g. aeruginosus from the 

 Tibesti Area of the Chad, all represent populations of gerbils of small 

 body and cranial size. These common characters may indicate taxo- 



