92 The Ottawa Naturalist. [November 



exceptional opportunities for study, owing to their abundance, and to 

 the fact that the}- do not burrow but remain above the ground. 



They are thick, low set animals, of a dark brownish color, darker 

 over the back, caused by the glossy guard hairs, becoming lighter on 

 the sides and reaching their extreme paleness on the under parts. 

 Their legs are short and sturdy, the eyes normal, the ears are small*, 

 and the tail is short, but seldom if ever shorter than the hind foot. 

 Their average size, taken from man}' specimens in my collection, is the 

 following: Length, 144 mm,; tail, 31 K; mm.; foot, 20 mm. All of 

 these characters are, however, subject to variation and slight depart- 

 ures, at least, can be expected. 



The above species is very closely related to those of the genus 

 Synaptomys and Phenacomys but its certain identity is made possible 

 by constant and distinct cranial and dental characters. An important 

 difference, and one most readily appreciated, if the skull is available, 

 is the formation of the teeth. In Synaptomys the upper incisors are 

 grooved, while the lower incisors are rooted on the inside of the molars 

 and terminate opposite the posterior molar. Microtus, on the other 

 hand, has no grooves on the upper incisors, and the lower incisors 

 cross the line of the molar series between the second and third molars 

 and terminate in the ascending ramus of the mandible behind the 

 posterior molar. This and the preceding genus have in common, root- 

 less molars. Phenacomys has upper incisors ungrooved similar to 

 Microtus, but the molars in contradistinction to the latter are rooted. 



The genus Microtus enjoys a circumpolar distribution and ranges 

 over its entire area, Old and New World, from the tropic's edge to the 

 northern-most fringe of mammalian life. The species (Microtus 

 pennsylvanicus) is, however, peculiar to America, and the animal we 

 know so well throughout Ontario. 



This vole becomes at times a menace to agricultural interests, 

 as it is a prolific breeder, bringing forth three or four litters of young 

 a season, with from four to eight young to the litter. Scarcely a month 

 from April to September but nests of young have been found, and 

 when a region becomes over-run the} - migrate over to other parts of 

 the country, giving rise in years of abnormal increase to "vole plagues" 

 which are so devastating to crops the country over. They are truly 

 the most destructive of all small animals. Their tastes, while essen- 

 tially vegeterian, sometimes, no doubt, become carnivorous, as they 

 may readily be trapped by means of a meat bait. 



They naturally love the low meadows and grass lands where rank 

 vegetation flourishes, giving them the seclusion the} 7 seek. Here they 

 drive their intricate system of runways and tunnelings over the ground, 

 forming a perfect maze of passages, running in all directions, crossing 

 and recrossing. 



*In the summer the ears are longer than the fur; in the winter the 

 longer fur conceals the ears. C.G.H. 



