﻿42 



NORTH AMERICAN FAUNA. 



[No. 12. 



External form. — In external form the species of Phenacomys show no 

 peculiarities to distinguish them from the other voles. The body, tail, 

 feet, ears, and eyes are usually proportioned about as in Microtus arva- 

 lis or M. austerus. In P. longicauda, however, the tail is proportionally 

 longer than in any of the other known species. 



General remarks. — Phenacomys is readily distinguished from Microtus 

 by the rooted molars. From PJvotomys, Phenacomys is separated by 

 certain characters in the form of the skull, and more especially of the 

 bony palate, as well as by peculiarities in the teeth. The differences 

 between the three genera may be compared in detail as follows: 



Microtus. 



Eoot of lower incisor above den- 

 tal foramen. 

 Molars rootless throughout life.. 



Molais large and strong, the 

 salient angles sharp. 



Keentrant angles on outer and 

 inner sides of lower molars ap- 

 proximately equal in depth. 



Skull strong and angular 



Posterior border of bony palate 

 extremely variable. 



Middle portion of 

 tinctly expanded. 



rgoma dis- 



Evotomys. 



Phenacomys. 



Root of lower incisor below den- 

 tal foramen. 



Molars rooted in the adult, the 

 roots closed in extreme old 

 age. 



Molars small and weak, the sal- 

 ient angle rounded. 



Reentrant angles on outer and 

 inner sides of lower molars 

 approximately equal in depth. 



Skull weak and rounded 



Posterior border of bony palate 

 a thin -edged shelf continuous 

 between alveoli of posterior 

 molars. 



Middle portion of zygoma 

 scarcely expanded. 



Eoot of lower incisor bolow den- 

 tal foramen. 



Molars rooted in the adult, the 

 roots closed in extreme old age. 



Molars large and strong, the sal- 

 ient angles sharp. 



Reentrant angles on inner side of 

 lower molars very much deeper 

 than those on outer side. 



Skull strong and angular. 



Posterior border of palate never 

 a thin-edged shelf. 



Middle portion of zygoma dis- 

 tinctly expanded. 



Since the discovery of the genus Phenacomys the following species 

 have been described: P. intermedius Merriam, P. celatus Merriam, P. 

 ungava Merriam, P. latimanus Merriam, P. orophilus Merriam, P. longi- 

 cauda True, P. truei Allen, and P. oramontis Ehoads. The status of 

 these forms is wholly a matter of conjecture. 



Genus EVOTOMYS Coues. 



1839. Myodes DeS61ys Longcliamps, fitudes de Micromammalogie, p. 87, 1839 (sec- 



tion). 



1883. Myodes Lataste, Le Naturaliste, Tome II, p. 349, 1883 (subgenus). 



1840. Hypudceus Keyserling and Blasius, Die Wirbelthiere. Europas, p. 34, 1840 (sub- 



genus). Type Mus glareolus Schreber. (Not Hypudmis Illiger, 1811.) 

 1857. Hypudanis Baird, Mamm. N. Am., p. 513, 1857 (subgenus). 



1874. Evotomys Coues, Proc. Acad. Nat. Sci. Phila., p. 186, 1874 (genusj. Type Mm 

 rutilus Pall 



Geographic distrihution of type species. — Arctic region in Europe and 

 Asia, possibly in America also. 



Geographic distrihution of genus. — Boreal i^^orth America, Asia, and 

 Europe. 



