﻿July, 1896.] 



KEYS TO SUBGENERA. 



31 



m 3 with 2 closed triangles. 



Triangles in m 3 alternate and closed. 



Aquatic; soles naked; tail long Neofiber 



Not aquatic ; soles hairy ; tail short Lagurus 



Triangles in m 3 normally opposite and open. 



Claws small, those on hind feet always longest. 

 Mammee 8 ; foot pads 5. 



Small; not aquatic; fur shore Chilotus 



{Large; aquatic; fur Jong Arvicola) 



(Mammce 4; footyads 5; skull high Pedomys) 



{Claws large, those on front feet often longest.) 



{Fur short and dense Pitijmys) 



{Fur long and soft Phaiomys) 



m 1 with 4 closed triangles. 



m 3 with posterior loop elongated in axis of jaw. 



Skull broad and flat ; plantar tubercles 5 Hyperacrius 



Skull not broad and flat ; plantar tubercles 6 Alticola 



(m 3 xvlth j)osterior loop rounded or crescentic.) 



{m 3 with 3 clos&d triangles Aficrotus) 



{m 3 tvith S closed triangles Arricola) 



m 1 with 3 closed triangles. 



{m 3 ivith 3 closed triangles.) 



{Plantar tubercles G.) 



{Posterior loop of m 3 short or strongly curred; palate normal . .. Microtus) 

 {Posterior loop of m 3 long and straight; palate ahnormal Alticola) 



{Plantar tubercles 5.) 



{Mammw 8; palate normal Arvicola) 



{Mammal 4; palate abnormal Hyperacrius) 



m 3 with 2 closed triangles. 



Sole almost naked Arvicola 



Sole hairy. 



{Palate abnormal Hyperacrius) 



Palate normal. 



Claws long, all about equal in length Phaiomys 



Claws short, those on front feet shortest Pedomys 



{m 3 with 1 closed triangle Hyperacrius) 



m 1 with 0 closed triangles. 



m 2 and m 3 of approximately the same form Eothenomys 



m 2 and m 3 very dilferent in form Anteliomys 



7. KEY TO THP: SUBGENERA OF MICROTUS. 



[Based primarily on mamrafe and foot pads.] 



Mamma) 10 Phaiomys 



MammtB 8. 



Plantar tubercles 6. 



Palato normal Microtus 



Palate abnormal A Iticola 



Plantar tubercles 5. 



Conspicuous musk glands on sides Arricola 



No musk glands on sides. 



Color dark brown Chilotus 



Color light grayish or yellowish Lagurus 



