New Species and Subspecies of Voles. 87 



General characters. Size large ; ears small ; tail rather short ; fur coarse 

 and lax ; colors dark ; hip glands conspicuous in adult males. Skull mas 

 sive and angular; incisive foramina narrow and closing to a point pos 

 teriorly. 



Color. March specimens: Above dark sepia or bister, much obscured by 

 blackish hairs; sides lighter; belly smoky gray; feet dark gray; tail in 

 distinctly bicolor, blackish above, gray or brownish below; lips usually 

 white; tip of nose in adult usually whitish. Young with a blackish 

 dorsal stripe and dusky feet and tail. 



Cranial characters. Skull heavy, angular, and much ridged ; frontals 

 high; rostrum bent downward; incisive foramina short, rather narrow 

 and constricted to a point posteriorly; dentition heavy; upper incisors 

 curved abruptly downward; first upper molar with 5 closed triangles; 

 second with 4 triangles in 8 out of 16 specimens; in the other 8, with a 

 slight inner lobe or loop at base of posterior triangle ; third with anterior 

 crescent, three closed triangles and a posterior loop with two inner lobes 

 or horns. 



Measurements. Type specimen : Total length 210; tail vertebrae 55 ; hind 

 foot 25.5. Average of 8 specimens from type locality : Total length 176; 

 tail vertebrae 47 ; hind foot 23. Skull of type : Basal length 32 ; nasals 10.2 ; 

 zygomatic breadth 19.3; mastoid breadth 14.3; alveolar length of upper 

 molar series 8. 



Microtus nevadensis rivularis subsp. nov. 



Type from St. George, Utah, No. y|*, g ad., Merriam Coll. Collected 

 Jan. 6, 1889, by Vernon Bailey. Orig. No. 493. 



General characters. Smaller and lighter colored than its nearest rela 

 tive, M. nevadensis; skull less rigid and angular; bullse larger ; incisive 

 foramina longer and narrower; ears small, nearly concealed by fur. 



Color. Winter pelage : Upper parts dull bister, darkened with blackish 

 tipped hairs (similar to californicus) ; sides scarcely paler; belly washed 

 with whitish ; feet dull grayish ; tail bicolor, grayish below, blackish 

 above. Young darker than adults, but not black backed. 



Cranial characters. Skull smaller and slenderer than skulls of nevadensis 

 of equal age ; audital bullae much larger and fuller ; anterior end of basi- 

 occipital narrower ; incisive foramina narrower and actually as well as 

 relatively longer ; angular process of lower jaw longer and slenderer ; in 

 cisors much slenderer ; molar pattern essentially the same. 



Measurements. Type : Total length 179 ; tail vertebrae 48 ; hind foot 23. 

 Skull of type: Basal length 28.2 ; nasals 8.3 ; zygomatic breadth 17 ; mas 

 toid breadth 13.3 ; alveolar length of upper molar series 7.3. 



Microtus nanus canescens subsp. nov. 



Type from Conconully, Washington. No. 90577, $ ad., U. S. Nat. Mus., 

 Biological Survey Coll. Collected Sept. 12, 1897, by J. Alden Loring. 

 Orig. No. 4654. 



