110 U.S. NATIONAL MUSEUM BULLETIN 275 



from those from the type locality. Apparently, the low-lying areas 

 associated with the Wadi Natroun, Qattara Depression, Siwa Oasis, 

 and Bahr el Tubat provide a continuum of suitable habitat linking 

 these various populations together. 



In some characters, notably heavy zygomata, large and ventrally 

 inflated auditory bullae, narrow basioccipital and small body size, 

 these gerbils from Giarabub show evidences of gene exchange with 

 G. g. psammophilous to the west. Apparently they are able to overcome 

 the barrier imposed by the Sand Sea of Calanscio in this region of 

 Libya. 



Some gerbils from Giarabub are noticeably darker, more orangish 

 in dorsal color, than others. This same feature was observed in jerboas 

 (Jaculus jaculus) from Giarabub and is presumably an adaptive 

 response to the different color of the sand in this area. 



Ecological observations. Giarabub Oasis is a portion of the 

 great depression formed from the east-west linkage of the Wadi 

 Natroun, Qattara Depression, and Siwa Oasis. Although located in 

 the interior of the desert, all three "sebchets" are below sea level. 

 Sandy areas of large extent have accumulated here and provide 

 desirable habitat for these gerbils. Plant cover is more abundant in 

 these low-lying areas than elsewhere; dense stands of Phragmites are 

 widespread in the bottoms of the depressions; and Tamarix occupies 

 the more elevated areas where the soil is firmer and more stable. 

 Various other species of woody shrubs are also present. Many resemble 

 the chenopods, woody composites, and thorny perennials of the 

 western United States. The series from Giarabub was obtained from 

 some large dunes near the oasis. 



A concentration of sandy-clay hummocks within a localized sandy 

 elevation of the valley floor formed the habitat at the collecting site 

 24 kilometers south-southeast of Giarabub. The vegetative cover here 

 was particularly dense and varied. 



Bahr el Tubat is a large, quite shallow, saline lake surrounded, in 

 some places, by dense stands of reeds and sedges. In other areas of the 

 shoreline, salty deposits of great thickness and extent occur, rendering 

 the habitat unsuitable for mammals. The specimens from Bahr el 

 Tubat were taken from a series of vegetated dunes beyond the lake and 

 slightly higher in elevation. 



Gerbillus gerbillus latastei Thomas and Trouessart 



Gerbillus gerbillus latastei Thomas and Trouessart, Bull. Soc. Zool. France, ser. 

 5, vol. 28, pp. 171-174, July 28, 1903 (Kebili, Southern Tunisia). 



Specimens examined. Three, from Tripolitania : 40 km N 

 Sinauen, 2; 5 km E Derg, 1. 



