118 U.S. NATIONAL MUSEUM BULLETIN 2 75 



of rather discontinuous populations throughout the northern Chad 

 and west-central Sudan. In the future, when more localities become 

 represented by specimens, it is probable that a more clearly defined 

 dispersal route, consisting of several overlapping populations, will 

 be found to unite the Libyan populations with those of the type 

 locality in the Nile Valley. 



Prior to the present study, Ellerman and Morrison-Scott (1951) 

 included Algeria within the range of G. p. pyramidum, based, appar- 

 ently, on specimens from El Golea and In Salah. It is now known 

 that the range of the nominate subspecies is confined to Egypt (in- 

 cluding Sinai) and Sudan as far south as Khartoum. The range of 

 G. p. tarabuli thus is interposed between the areas of occurrence of 

 these Algerian populations and the type locality. Such a discontinuous 

 distribution for members of the same subspecies is untenable, and I 

 suspect that these gerbils from central Algeria represent subspecies 

 distinct from those in Libya and Egypt. 



Gerbillus pyramidum hamadensis, new subspecies 



Holotype. Adult male, skin and skull, USNM 321827, from 5 km 

 E Derg, Tripolitania Province, Libya, obtained Nov. 14, 1961, by 

 G. L. Ranck, original no. 886. 



Specimens examined. Fifty-five, from Cyrenaica: 5 km W El 

 Agheila, 1; from Tripolitania: 5 km N Mizda, 3; 12 km W Sirte, 2; 

 15 km WNW Marble Arch, 3; 30 km S Bu Ngem, 2; 5 km E Derg, 

 13; 5 km S Socna, 15; Bir Fergian, 10 km S Socna, 17 (16 skin only). 



Measurements. Averages and extremes of six adult males and five 

 adult females from the type locality, with the measurements of the 

 type in brackets, are, respectively: Total length 240.2 (235-244), 228 

 (223-234), [244]; length of tail 141 (137-145), 131.4 (128-135), [145]; 

 length of hind foot 30.2 (29-32), 31 (29-32), [29]; length of ear 14.8 

 (14-16), 15.2 (14-16), [16]; occipitonasal length of skull 31.6 (31-32), 

 30.5 (29.7-31.4), [32]; length of auditory bulla 11.7 (11.4-11.9), 11.5 

 (11.2-11.7), [11.6]; crown length of upper molariform toothrow 4.3 

 (4.1-4.4), 4.2 (4-4.4), [4.2]; greatest breadth across zygomatic arches 

 16.7 (15.7-16.9), 16.2 (15.8-16.8), [16.6]; least interorbital breadth 

 6.5 (6-6.8), 6.3 (6-6.6), [6.8] : breadth of rostrum at level of antorbital 

 foramina 3.6 (3.5-3.8), 3.6 (3.5-3.8), [3.6], greatest length of nasals 

 12.3 (11.8-12.6), 11.7 (11.3-12), [12.6]. 



Diagnosis. Upperparts Cinnamon-Buff grading to Clay Color and 

 Tawny-Olive on rump and becoming paler on sides; entire dorsum 

 lightly washed with brownish hairs which project appreciably beyond 

 the paler colored underlying hairs; subauricular areas Cinnamon-Buff 

 with slight suffusion of grayish-brown hairs; supraorbital, rostral, 

 mystacial, circumoral, and pectoral areas pure white; postauricular 



