162 U.S. NATIONAL MUSEUM BULLETIN 2 75 



However, certain bushy-tailed forms, previously recognized as 

 Meriones libycus confalonierii de Beaux and Meriones libycus caudatus 

 Thomas, are sympatric with these coastal subspecies of M. libycus. 

 It therefore becomes necessary to separate these populations taxo- 

 nomically. Because the name caudatus is older, it is here raised from 

 subspecific status to full species rank. These populations may now be 

 referred to as Meriones caudatus caudatus and Meriones caudatus 

 confalonierii. 



The jirds of Libya are here considered to be represented by the 

 following three species and seven subspecies, three of which are here 

 described as new: Meriones caudatus amplus; Meriones caudatus cau- 

 datus; Meriones caudatus confalonierii; Meriones caudatus luridus; 

 Meriones crassus tripolius; Meriones libycus auratus; and Meriones 

 libycus azizi. 



The size and shape of the suprameatal triangle and the amount of 

 closure of the latter by the enveloping processes of the supraoccipital 

 and temporal bones varies among the three species of Meriones and 

 serves to readily separate them. In M. crassus, the suprameatal tri- 

 angles are markedly larger than those of M. caudatus and M. libycus 

 and are open behind rather than completely or partially enclosed by 

 the supraoccipital and temporal bones. The suprameatal triangles are 

 of comparable size in M. caudatus and M. libycus, but in M. caudatus 

 the closure of the suprameatal triangles is complete, whereas in M. 

 libycus it is usually imperfect. 



Individual genetic variation (nongeographic) is relatively high 

 among populations of jirds in Libya, yet the peculiar physiography 

 has resulted in the formation of several distinct subspecies. Morpho- 

 logical features most frequently associated with geographical dis- 

 tribution include differences in the length of the skull, palate, and 

 nasals, and changes in the shape and size of the audital and mastoidal 

 portions of the auditory bullae. In addition to cranial characters, the 

 size and general form of external features are taxonomically important. 

 Color, although sometimes highly variable within a given population, 

 is frequently useful in differentiating the various subspecies. 



The subspecies of the several species of Meriones, especially those 

 of M. caudatus, are generally more sharply defined morphologically 

 than those of the various species of Gerbillus. This apparent morpho- 

 logical segregation in Meriones may be misleading, inasmuch as the 

 samples representing the subspecies are much smaller than those 

 available for Gerbillus and may not demonstrate the complete range 

 of variation for any given character. 



Of the three species of Meriones occurring in Libya, only Meriones 

 caudatus is represented by samples of sufficient size to justify statistical 

 analysis at the infraspecific level. 



