RODENTS OF LIBYA 95 



three localities in northern Tripolitania. Setzer (1957) recognized G. 

 eatoni as a full species largely on the characters established by Thomas. 

 He collected both species from 5 kilometers west of El Agheila, and 

 in the present study, G. gerbillus and G. eatoni were found to occur 

 together at several localities in coastal Tripolitania and Cyrenaica 

 without any evidence of interbreeding. The present study indicates 

 that G. eatoni is a fidl species and can be distinguished from other 

 species of Gerbillus by the same diagnostic characters as set forth by 

 Thomas and by Setzer. 



Although this species is not abundant in Libya, and large series 

 are lacking, local differentiation has occurred sufficiently to warrant 

 the recognition of three distinct subspecies, each restricted to a 

 particular portion of the Libyan coastal plain. In Libya, the range of 

 this species probably includes all of the coastal regions and in many 

 areas, the transitory desert associated with the coastal escarpment. 

 It is unknown from the Saharan interior where G. gerbillus is the 

 dominant species. 



Ecological observations. These gerbils are usually found in 

 areas of loose sand on the coastal plain but frequently occur in habi- 

 tats lacking sand. In many areas the coastal plain is reduced to a 

 narrow fringe of desolate beach or is entirely eliminated. Thus, these 

 coastal populations of gerbils sometimes occur in a variety of eco- 

 logical conditions. 



Throughout their range in Libya these gerbils occur with several 

 species of jirds (Meriones) and jerboas (Jaculus), fat-tailed sand rats 

 (Pachyuromys) , and gerbils of the subgenus Dipodillus. 



Gerbillus eatoni eatoni Thomas 



Gerbillus eatoni Thomas, Proc. Zool. Soc. London, vol. 2, pt. 1, p. 6, October 

 1902 (El Cusher, Tripolitania Province, Libya). 



Specimens examined. Twenty-five, from Cyrenaica: 4 km W 

 Gheminez, 6; 10 km S Agedabia, 8; 5 km W El Agheila, 4 (2 skin 

 only); from Tripolitania: 5 km W Sirte, 4; El Cusher, 1 (subadult 

 BM) ; 15 km WNW Marble Arch, 2. 



Measurements. Averages and extremes of three males and four 

 females from 10 kilometers south of Agedabia, Cyrenaica Province, 

 are, respectively: Total length 214 (208-218), 214.8 (210-222); length 

 of tail 124.3 (117-131), 124.5 (122-126); length of hind foot 27.7 

 (27-28), 27.3 (26-29); length of ear 14.3 (13-15), 14.5 (13-15); 

 occipitonasal length of skull 28.5 (28.1-28.9), 28.4 (28.1-28.7); length 

 of auditory bulla 10.6 (10.5-10.7), 10.5 (10.3-10.6); crown length of 

 upper molariform toothrow 4 (4-4.1), 4 (3.9-4.2); greatest breadth 

 across zygomatic arches 15.2 (15-15.3), 15.4 (15.1-15.6) ; least inter- 

 orbital breadth 5.7 (5.6-5.7), 5.6 (5.4-5.7); breadth of rostrum at 



