70 U.S. NATIONAL MUSEUM BULLETIN 2 75 



Measurements. The measurements of two immature males, 

 325019 and 325021, and of an adult male, 325020, from 5 kilometers 

 west of Tocra, Cyrenaica, are respectively: Total length 131, 130, 130; 

 length of tail 30, 25, 31 ; length of hind foot 18, ?, 18; length of ear 1 1, 

 10, 12; condyloincisive length of skull 24.6, 25.8, 26.5; greatest breadth 

 across zygomatic arches 14.4, 14.5, 15.9; length of nasals 6.7, 6.9, 6.7; least 

 interorbital breadth 3.7, 3.9, 3.8; crown length of upper molariform 

 toothrow 5.9, 6.4, 6.4; greatest breadth across braincase 11.4, 11.7, 12; 

 length of incisive foramina 4.4, 4.5, 4.5. 



Diagnosis. Entire dorsum uniformly colored Buckthorn Brown, 

 becoming slightly paler on flanks and sides and forming a distinct con- 

 trast with the white-tipped hairs of the venter ; all hairs of dorsum and 

 venter Plumbeous basally; pinnae of ears short and inconspicuous, 

 Prout's Brown, sparsely haired, and with several long brownish hairs 

 partially covering ventrolateral surfaces; eye ring absent; vibrissae 

 relatively short and fine and composed of both light and dark individ- 

 ual hairs; dorsal surfaces of forelegs, hindlegs, and feet light tan; 

 ventral surfaces of fore and hind feet naked with prominent carpal and 

 palmar tubercles; front feet with four functional digits with claws, the 

 first digit reduced to a rudimentary tubercle; hind feet with five func- 

 tional digits with claws; tail noticeably short and distinctly bicolored 

 dark brown above and buff below. Skull: Medium in size; compact 

 and angular; zygomata heavy with a uniform lateral curvature; inter- 

 orbital breadth markedly constricted; suprameatal portion of auditory 

 bulla enclosed by processes of the supraoccipital and temporal bones; 

 parietal ridges markedly reduced and inconspicuous; interparietal 

 transversely elongated ; nasals short and moderately flaring anteriorly ; 

 upper incisors markedly prognathous; dorsal margin of foramen 

 magnum with prominent notch; audital portions of auditory bullae 

 conspicuously inflated ventrally; pterygoid processes and external 

 pterygoid fossae heavily fenestrated; hamulae large and applied to 

 anteromedial portions of auditory bullae; molariform toothrows long 

 and individual teeth with prominent inner and outer salient angles; 

 anterior palatine foramina relatively short and narrow; posterior 

 palatine canals small and inconspicuous. 



Comparisons. Compared to representatives of Microtus guentheri 

 Danford and Alston from the Valley of Ali Bey Dere, near Piringcikov, 

 16 kilometers west of Istanbul, Turkey, the specimens from Libya 

 differ strikingly in having markedly smaller, less angular skulls, nar- 

 rower rostra, more ventrally inflated auditory bullae, more fragile 

 zygomata, narrower basioccipitals, markedly smaller incisors, and the 

 third molar nearly as large as the second, rather than being signifi- 

 cantly smaller as in guentheri. In external characters, the specimens 



