﻿50 



NORTH AMERICAN FAUNA. 



[No. 12. 



1881. Fremiomijs Polyakoff, Mem. Acad. Imp. Sci., St. P6tersbourg, XXXIX suppL, p. 

 34, 1881 (genus). Type Mus lagurus Pall. 



Geographic distrihution of type species. — Plateaus of western auci 

 central Asia. 



Oeograpliic distrihution of suhgenus. — The range of the subgenus 

 Lagiirus is very imperfectly known, but probably extends over a large 

 part of the Boreal region in Asia and in western North America. 



Essentia I characters: 



Palate slightly abnormal. 



m 3 normally with 2 or 3 tightly closed triangles. 



m 1 normally with 5 closed triangles and 8 or 9 salient angles. 



ra 3 normally with 2 or 3 closed triangles and 5 or 6 salient angles. 



Mamma?, 8. 



Plantar tubercles, 5. 



Sole Yery hairy. 



Claws on hind feet longest. 



Fnr not specially modihed. 



Sl'uU.—Th.e skull of Lagurus (PI. I, fig. 7^) may be at once recognized 

 by the form of tlie audita! bulla? (fig. 24). These are larger than in any 

 other subgenus of Microtus^ and are especially remarkable on account 

 of the way in which they project backward behind the plane of the 



occiput. Aside from the audital bulkne, 

 the skull does not differ very notice- 

 ably from that of Piti/iuys or Chilottis. 

 As compared with that of PitymySy 

 however, the rostrum is considerably 

 more slender. The dorsal outline is 

 flat, as in Chi lot us. 



Bony palate. — The bony palate (PI. 

 II, fig. 2) is normal in structure but 

 there is less difference than usual between the levels of the portions 

 lying in front of and behind the lateral bridges. A peculiar flat palate 

 with shallow lateral pits and broad, ill-defined median sloping ridge 

 is the result. This form of palate is much like that of Fhenacomys 

 (PL II, fig. 1). 



Enamel pattern in 

 general. — The enamel 



Fig. 24.— Audital bullag, (a) Microtvs {Mi- 

 crofus) arvalis {b) M, {Lagurus) pallidus. 

 (x 2.) 



pattern of Lagurus 

 (fig. 25) is character- 

 ized by the tight clos- 

 ure of all triangles, 

 notably in the back 

 lower molar, and the 

 great width of the reentrant angles. 



Fig. 25. — Enamel pattern of molar teeth: (a) Mierotus {Lagurus) 

 2)aUiclus; {b) 21. {L.) lagurus ; (c) 21. {L.) luteus. (x5.) 



The latter peculiarity gives the 



^See also Naturwissenschaftliche Eesultate der von . M. Przewalski unternom- 

 menen Eeisen, PI. XIII, figs. 1, 2, 3, 12, 13, and 11. 



