RODENTS OF LIBYA 211 



as a strict commensal but regarded it as a monotypic species with a 

 range confined to the Nile Valley and distinguishable from A. dimi- 

 diatus by more flattened braincase, more rounded foramen magnum, 

 more nearly vertical (less recurved) upper incisors, and broader and 

 less elongated pterygoid fossae. 



The above differences are apparent when spiny mice from Sinai and 

 Baluchistan, Iran, are compared to those from the Nile Delta, but 

 specimens from Libya do not show these same differences, and there 

 is too much overlap of characters among populations of these mice 

 from Libya and the Nile Valley to suggest specific differences. I agree 

 with Setzer that the "cahirinus group" is divisible into two species, 

 A. cahirinus and A. dimidiatus, but extend the range of A. cahirinus 

 to include Libya, as well as the Nile Valley of Egypt, and limit the 

 range of A. dimidiatus to areas to the south, east, and north. For the 

 present, until a thorough revisionary work of this poorly understood 

 genus has been undertaken, I prefer to include the spiny mice of 

 Libya and the commensal forms of the Nile Valley of Egypt within 

 a single species, Acomys cahirinus. Commensalism is unknown in the 

 Libyan populations, but this is not a valid criterion for specific 

 designation and could have arisen independently in the populations 

 of spiny mice in the Nile Valley. 



Cranially, two specimens from El Barcat in the extreme south- 

 western Fezzan resemble those from Cufra but differ in having more 

 flattened and wider braincases, shorter anterior palatine foramina, 

 wider rostra, and shorter nasals. In color, they more closely resemble 

 the two specimens from Socna but are slightly more grayish dorsally 

 and are darker on the ventral surface of the tail. It is apparent that 

 these two specimens from the Fezzan represent a population of spiny 

 mice differing significantly from others in Libya, For the present, 

 however, until larger series are obtained from the vicinity of El Barcat 

 and Ghat, in the Fezzan, and more topotypes of A. c. viator become 

 available from Tripolitania, these two specimens are provisionally 

 referred to A. c. viator largely on the grounds of geographic occurrence. 



I have not examined specimens of Acomys cahirinus seurati Heim de 

 Balsac, the type locality of which is Iniker, in the Ahaggar Mountains 

 of southern Algeria, but the spiny mice from the Fezzan may represent 

 this subspecies. 



Ecological observations. Spiny mice were obtained from areas 

 of loose sand, littered with dead fronds and debris, near the bases of 

 date palms. 



According to Thomas (1902, p. 11), spiny mice from the Wadi 

 Sultan near Socna resembled in color "the small blackish stones 

 which lie about among the Soda Mountains." This statement sug- 

 gests that the habitat in the Wadi Sultan was primarily of a rocky 

 character. 



