404 



INTRODUCTION TO ZOOLOGY. 



points exhibit a greater affinity to the Beaver than to the 

 Mouse, with which in popular language they are associated. 

 Of these there are in England three species; yet the genus 

 (Arvicola) to which they belong, is altogether unrepresented 

 in Ireland.* 



Fig. 305. SHORT-TAILED FIELD MOUSE. 



Teeth. We turn from the geographical distribution of the 

 Rodentia to the most striking characteristic of the order, the 

 structure of the teeth. The Molar or grinding teeth, have 



Fig. 306. MOLAR TEETH OF THE 

 ARVICOLA. 



Fig. 307. MOLAR TEETH OF THE 

 BEAVER. 



ridges of enamel variously arranged (Fig. 306, 307), which 

 keep up the inequality of surface, as they wear less rapidly 

 than the other portions. The incisor teeth, with their chisel- 

 shaped edges, are however more remarkable. If a carpenter 

 could lay hold of the wishing-cap of the fairy tale, and desire 



* The number actually recorded in the History of British Quadrupeds 

 is fifteen; but since the publication of that valuable and beautifully illus- 

 trated work, Mr. W. Thompson has taken one from the number, by 

 showing that the Irish and the Alpine Hare, instead of being distinct, are 

 one species. To the "Report" of the latter gentleman on the Fauna of 

 Ireland, we are indebted for the means of enumerating the British species 

 which are not indigenous in Ireland. They are 



1. The Squirrel (?) 



2. The Dormouse 



3. The Harvest Mouse (?) 



4. The Water Vole 



5. The Field Yole 



6. The Bank Vole 



7. The Common Hare 



Scinrus vulgaris). 



Myoxus avellanarius). 

 (Mus messorius). 

 (Arvicola amphibius*). 

 (Arvicola agrestis). 

 (Arvicola pratensis). 

 (Lepus timidus). 





