Prof. A. Nehring on Myodes lemmus crassidens. 295 



these lemmings beside that of an Arvicola amphibius or 

 A. ratticeps in order to appreciate the great difference. 



Fi-. 1. 



Fi-. 2. 



Fig. 1. — The masticatory surfaces of the cheek-teeth of Myodes lemmus 

 crassidens from Portugal, enlarged about 6 times. 



ti. Lower row of teeth. o. Upper row of teeth. 



Fig. 2. — The masticatoiy surfaces of the cheek-teeth of Ariicola ratticeps, 

 K. & Bl., from Northern Russia, enlarged 6 times. 



M. Lower row of teeth. o. Upper row of teeth. 



Fi-. 3. 



The skull of Myodes lemmus crassidens, w^ith the under jaw, 

 from Portup-al. Natural size. 



The differences between the three known species of lemmings 

 lie chiefly in the colour of the fur and in their size. Fix)ra my 



