3S8 



IKTEODUCTION TO ZOOLOGY. 



sents one of the Voles, little animals, vvhicli in many 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 {Arvi- 

 cola) to which they belong, is altogether unrepresented in 

 Ireland.* 



Fic 30.J.— Shoi;t-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. 30C. — MoLAE Telth of the 

 Arvicola. 



Fig. 307.— Molar Teeth of the 

 Beaver. 



ridges of enamel variously arranged {Fig. 306, 307), w^hich 

 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 



* 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. \s'. Thompson has taken one from the number, by sliowing 

 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 (V) 



2. The Dormouse 



3. The Harvest Mouse 



4. The "Water Vole 



5. The Field Vole 



6. The Bank Vole 



7. The Common Hare. 



(Sciurvs vulgaris). 

 {^Myoxus avellanarius). 

 (?) (^Mns messorms). 



(^Arvicola amphibius). 

 (^Arvicola agrestis). 

 (^Arvicola praiensis). 

 (Lepus timidus). 



tr. 



