156 U.S. NATIONAL MUSEUM BULLETIN 2 75 



and longer ears. These specimens from Rnmia are also darker in dorsal 

 color, including the tail, and have a more marbled appearance dorsally, 

 owing to a much stronger suffusion of brownish hairs. 



Compared to specimens from Rumia, specimen, 321831, from 5 

 kilometers east of Derg and another specimen, 321832, from 55 kilo- 

 meters SW of Bir Allagh, Tripolitania, have a more streaked pelage, 

 and the dorsal lip of the external auditory meatus is more inflated 

 and more closely applied to the squamous portion of the temporal. 

 In the above characters, these two specimens resemble P. d. duprasi of 

 Algeria, but in all other characters, they are closer to P. d. natronensis. 

 Toschi (1951) referred a specimen from Bir el Fatia, Fezzan Province, 

 to P. d. duprasi. He apparently based this assignment largely on 

 geographic grounds, as the measurements of this specimen are much 

 closer to those of topo types of P. d. natronensis. 



Specimens from the coastal plain of the Gulf of Sirte in Tripolitania 

 are the palest in dorsal color and have the smallest hind feet of all 

 representatives of this species in Libya. 



In view of the rather wide range of this species in Libya, specimens 

 from the various localities are remarkably uniform morphologically. 

 These similarities suggest a relatively constant genetic interchange 

 among the various populations rendered possible by the continuity of 

 suitable habitat throughout most of coastal Libya. With the exception 

 of two specimens, 321831 and 321832, from western Tripolitania, a 

 single specimen from Bir el Fatia in the Fezzan (Toschi, 1951), and 

 a specimen, 325582, from the Gebel el Harug el Asued of central 

 Cyrenaica, this species in Libya is almost exclusively restricted to 

 localities near the coast. The comparatively few specimens available 

 at the present time cannot serve as a reliable index to their distribution 

 in Libya, and their range doubtless includes a much greater portion 

 of the interior than presently is supposed. 



A single adult male specimen, 325582, from the Wadi er Rueis, 

 Gebel el Harug el Asued, central Cyrenaica, is the southernmost record 

 for this species in Libya, and it differs strikingly from all other rep- 

 resentatives of this species in Libya by much paler dorsal color and 

 markedly smaller size of all measurements. Unfortunately, the pelage 

 of this specimen is badly worn, and the skull is badly broken rendering 

 certain cranial measurements unavailable. If this specimen is typical 

 of those comprising the population in this region of Cyrenaica, it 

 clearly represents a new subspecies. The jerboas (Jaculus deserti 

 vastus) of this isolated region have also undergone significant changes 

 in size and cranial dimensions. A moderate amount of morphological 

 divergence is not uncommon among populations of geographic isolates. 



Ecological observations. The range of fat-tailed sand rats, in 

 Libya, closely corresponds to that of several other species of rodents, 



