848 



Genus EPIMYS Trouessart. 



1857. Mus Blasius, Saugethiere Deutschlands, p. 309 (part). 



1867. Rattus Fitzinger, Sitzungsber. kais. Akad. Wissensch. Wien, Math.- 



Naturwiss. Classe, lvi, p. 6.3 (not of Donovan, 1827). 

 1881. Epimys Trouessart, Bull. Soc. d'Etudes Sci. d'Angers, x. p. 117 



(sub-genus). Type by subsequent selection Mus rattus Linnaeus. 

 1910. Epimys Miller, Proc. Biol. Soc. Washington, xxiii, p. 58, April 19, 



1910. 



Ti/pe species. — Mus rattus Linnteus. 



Geographical distribution. — Originally confined to the temperate 

 and tropical portions of the Old AVorld, but now essentially 

 cosmopolitan through the artificial dispersal of two species. 



Characters. — External form, skull, and teeth with no special 

 modifications ; molars slightly graduated in size from first to 

 third, the anterior tooth not tending to assume the main 

 function of the tooth-row, the posterior tooth not tending to 

 disappear ; enamel foldings of upper molars directly referable to 

 a simple 9-cusped pattern and its reductions, the outer margin of 

 m^ and in^ never with more than three cusps, the inner margin 

 of the same teeth never with more than two cusps ; m^ with five 

 roots, its first lamina not distorted by the backward displacement 

 ol tl ; upper incisor compressed, set at such an angle that its 

 outer side is worn smoothly away by action of lower teeth. 



Remarlcs. — The genus Epimys is the most widely distributed 

 and abundantly represented group in the sub-family Mnrinse. 

 As here defined it contains the great mass of the Asiatic, 

 Malayan and African species, several hundred in number, to 

 which the generic name Mus has during recent years gradually 

 become restricted. Only two of these occur in Europe. 



KEY TO THE EUROPEAN FORMS OP EPIMYS. 



Greatest breadth of brain-case across lateral ridges 

 about equal to length of parietal measured 

 along ridge ; first lamina of ■?»' and terminal 

 heel of w- with no well developed outer 

 tubercle ; external form rather heavy ; tail 

 decidedly shorter than head and body (Nor- 

 way rat) E. norvegiciis, p. 858. 



Greatest breadth of brain-case across lateral ridges 

 decidedly more than length of parietal mea- 

 sured along ridge; first lamina of »i' with 

 distinct outer tubercle usuallj' almost as large 

 as inner tubercle ; terminal heel of m- with 

 evident though incompletely separated outer 

 tubercle ; external form slender ; tail about 

 equal to head and body (usually a little longer) E. rattus, p. 849. 

 General colour slaty black, the underparts dark 



slaty grey (Distribution general) E. ,: raitu.-;. p. 853. 



General colour brown, the underparts buffy or 



greyish (Southern) H. r. alexaixln'nux, p. 854. 



