RODENTS OF LIBYA 189 



momys tripolitanus]) ; Zauia Mechili (de Beaux, 1938 [Psammomys 

 tripolitanus]); Tripolitania: Wadi Aggar, Wadi Cheggar (Thomas, 

 1902 [Psammomys tripolitanus]). 



Comparisons. Psammomys obesus can be readily distinguished from 

 Psammomys vexillaris by its darker color and greater size in all di- 

 mensions. 



Remarks. Superficially, members of this genus resemble those of 

 the genus Merion.es but upon closer scrutiny can be easily identified 

 by their plain, rather than distinctly grooved, upper incisors and 

 generally heavier, more angular skulls. Furthermore, representatives 

 of the genus Psammomys are primarily diurnal, whereas jirds (Meriones) 

 tend to be almost exclusively nocturnal in their habits. 



Specimens of Psammomys obesus obesus from coastal Libya east 

 of the Cyrenaican Plateau do not differ appreciably from those 

 representing Psammomys obesus obesus from farther east in Egypt. 

 The few specimens from the coastal plain along the Gulf of Sirte, 

 however, differ significantly from representatives of P. o. obesus 

 from Egypt and are here referred to Psamrnomys obesus tripolitanus. 



Ecological observations. In Libya, these large rodents are 

 limited in distribution to a rather narrow belt of alluvial soils and 

 abundant vegetation, which occurs along the coastal plain and 

 occasionally farther inland in portions of the transitional deserts. 

 At present, specimens are not available from the coastal plain of 

 Tripolitania, but doubtless this species occurs here also. These rodents 

 have a similar distribution in Egypt. 



All specimens I collected were from the more alluvial soils of the 

 shoulders of the road. As presently understood, these animals are 

 exclusively diurnal in their habits, emerging from their burrows 

 shortly after dawn, remaining active somewhat irregularly throughout 

 the day, and retiring to their burrows shortly after sunset. They dig 

 large burrows with conspicuous, well-worn entrances, usually marked 

 by piles of freshly deposited talus covered with seeds and bits of 

 local plants. They seem to prefer the loose soils of the elevated roadbed 

 or nearby large hillocks with a dense vegetative cover. 



Frequently, during the daytime, they are seen scurrying across the 

 road or running about the mounds while foraging. Diurnal traplines 

 were surprisingly ineffective and only rarely were fully adult animals 

 caught. On one occasion east of Tobruch, these diurnal traps were left 

 in position throughout the night and produced three jirds (Meriones) . 

 The occurrence of these jirds in the same trapline suggests that mem- 

 bers of these two genera occur together in the same burrow complexes. 

 The jirds, however, forage at night and the sand rats (Psammomys) 

 feed only during the hours of daylight. 



