﻿CONTENTS. 



Page 



Introduction 7 



The subfamily Microthm and its main divisions 8 



List of genera and subgenera of MicroUnce 9 



Geographic distribution 9 



Habits 10 



Nomenclature 11 



History of former classificatious 19 



Characters on which tlie present classification of the subgenera of Mieroius is 



based 24 



Keys 28 



Descriptions of living genera and subgenera 32 



Descriptions of extinct genera and subgenera 73 



Note on 'Arvicola' intermedius Newton 75 



ILLUSTRATIONS. 



PLATES. 



1. Skulls of Microtus inacropus, M. 2^>>i('to7Uim, AT. arvalis, AT. curtatus, M. oregoni, AT. 



terrestris, Al. alhicanda, AI. fertilh, Erotomys gapperi, Plienacomys oramoniis, 

 Lemmus nigripes, Si/napftomi/s ivrangeli, S. helaletes, Dicrostonyx torquatus. 



2. Bony palates of rhenacomys, Jlicroins, Lagurus, Pitymys, Arvicola, Alticola, 



Anteliomys, Eothenomys, EvcAomys, Xeofthcr, Dicrostonyx, Lemmus, Fitcr. 



3. Mandibles of SynajJtomys, rhenacomys, Aficrotus, Evotomys. 



TEXT FIGURES. 



1. First upper molar of six specimens oi Alicrotus pennsylv aniens. 



2. Second upper molar of six specimens of Alicrotus pennsylvanicus. 



3. Third upper molar of eighteen specimens of Alicrotus pennsylvanicus, 



4. First lower molar of eighteen specimens of Alicrotus pennsylvanicus. 



5. Second lower molar of four specimens of Alicrotus xyennsytvanicus. 



6. Third lower molar of four specimens of Alicrotus pennsylvanicus. 



7. Palatal view of skull of Alicrotus arvalis and Evotomys gapperi. 



8. Enamel pattern of molar teeth of AS'j/??aj^iom2/s coo2>e)'i. 



9. Palatal view of skulls of Synaptomys and Alictomys. 



10. Enamel pattern of molar teeth of Synaptomys innuitus. 



11. Enamel pattern of molar teeth of Lemmus lemmus. 



12. Left front foot of Lemmus lemmus. 



5 



