194 MICROTUS. 



Measurements. "Average total length of four adults, 159-75; tail 

 vertebrae, 46; hind foot, 21.25; ear, 12.5." 



389. borealis. {Arvicola), Richards, Zool. Journ., 1828, p. 517. 



Rhoads, Proc. Acad. Nat. Scien., 1894, p. 286. 



Type locality. Great Bear Lake, Hudson Bay Territory. 



Geogr. Distr. Arctic America. Limits not known. 



Genl. Char. Small; tail shorter than head. Middle upper molar 

 without posterior fold. Posterior end of frontals long, slender, strap- 

 shaped; anterior corners of parietals pointed. 



Color. Above blackish gray; beneath lead gray; tail clove brown 

 above, grayish white beneath; feet clove brown mixed with white; 

 claws whitish. 



Measurements. Total length, 139; tail vertebrse, 25; hind foot, 15; 

 ear, 6. 



B. Laguras. 



Audital bullae very large, projecting backward behind the plane 

 of the occiput. Palate normal; third lower molar with all triangles 

 closed; upper third molar with two closed triangles and posterior 

 loop. Plantar tubercles, 5; mammae, 8; inguinal, 4; pectoral, 4. 



Fig. 39. MicROTus (Lagurus) curtatus. 

 No. 1519 Field Columbian Museum Coll. Enlarged %. 



Lower tooth row. 

 Enlarged 6 times. 



Upper tooth row. 

 Enlarged 6 times. 



