RODENTS OF LIBYA 155 



same color as the pelage of the dorsum, but with faint suffusions of 

 whitish hairs on ventral surface. Skull: Medium in size; flattened 

 dorsoventrally and wedge-shaped; parietal ridges poorly defined; 

 suprameatal triangles large and usually completely enclosed by 

 enveloping processes of the supraoccipital and temporal bones; 

 auditory bullae conspicuously enlarged and inflated ventrally; audital 

 portions of bullae extending posterior to mastoidal processes and 

 covering almost one-half of ventral surface of skull; meatal processes 

 markedly enlarged and projecting farther laterally than the squamous 

 portions of the temporal bones to which they are firmly adpressed; 

 mastoidal portions of bullae also markedly enlarged and bulbous, 

 and projecting conspicuously beyond the level of the occiput; pterygoid 

 processes relatively short; hamulae firmly applied to anterior surface 

 of the auditory bullae; anterior palatine foramina and posterior 

 palatine canals markedly enlarged and bowing laterally; zygomata 

 relatively delicate and slightly convergent anteriorly; lachrymals 

 relatively small. 



Comparisons. This species resembles Meriones libycus but can 

 easily be distinguished from it and from all other jirds by its markedly 

 shorter and heavier tail, larger auditory bullae, and more wedge- 

 shaped body. 



From a near topotype of Pachyuromys duprasi duprasi Lataste from 

 Ghardaia, Algeria, specimens from 20 kilometers east of Rumia, 

 Tripolitania, and those from various localities around the Gulf of Sirte, 

 differ in having more gracile and less robust skulls (particularly more 

 delicate zygomata), markedly larger posterior palatine canals, and 

 longer and narrower rostra. Most of the Libyan specimens are also 

 darker in dorsal color and smaller in external and cranial dimensions, 

 being of comparable or larger size in length of ears, crown length of 

 upper molariform toothrows, length of nasals, and length of auditory 

 bullae. 



A single specimen (skin only, BM, no. 39.2168) of Pachyuromys 

 duprasi faro ulti Thomas from Mecheria, western Algeria, is markedly 

 darker in dorsal color than the Libyan specimens and has silkier, more 

 lustrous pelage. Cranial comparisons are not possible at this time, but 

 presumably P. d. jar o ulti differs significantly from Libyan specimens, 

 as the range of the latter is confined to the High Plateau of 

 northern Algeria and is. geographically, far removed from the Libyan 

 populations. 



Remarks. Although the specimens from near Rumia, Tripolitania, 

 are clearly referable to Pachyuromys duprasi natronensis, they differ 

 from topotypes of the latter from Bir Victoria, Western Desert 

 Governorate, Egypt, in being larger in condylobasal length of skull, 

 and in having slightly larger auditory bullae, slightly wider zygomata, 



