of the District of Montreal. 305 



Suh genus Arvicola, 



Sub gen. char. Incisors |, canines none, molars ||=16. Mo- 

 lars with flat crowns and irregular plates of enamel ; front toes 

 with nails ; tail round, hairy, nearly as long as the body. 

 A. Xanthognatus. Meadow mouse. 

 A. gapperi ? Baird ! 



v.p.s. Length of head and body, 5j- inches to 8 inches, of tail 

 2 inches ; Incisors pale yellow exteriorly, brown ones subrotund 

 and rather larger. Molars (upper) with three grooves ; ears 

 circular ; whiskers long; fore feet 4 dactyle with rudimentary 

 thumbs as callosities ; claws small; hind feet 5-dactyle ; fur in 

 upper parts of body reddish yellow ; the hairs below the yellow 

 tips, shining grey or black ; sides of head fulvous ; under parts of 

 body silvery blueish grey, darkening into blackish grey on the 

 shoulders; a blackish brown stripe runs along the nose ; tail brown- 

 ish black above and white beneath. 



Genus Castor, 

 Gen. char. Incisors |, canines •^, molars f f=: 20. Molars with 

 flat crowns and sinerous, complicated ridges of enamel, one on the 

 inner edge and three on the outer edge of the upper teetli ; feet 5- 

 dactyle ; front toes short ; hind ones longer and pulmatel ; tail 

 long oval, flat and scaly ; an anal pouch filled with an unctuous 

 strong smelling secretion. 



C, fiber. The Beaver. 



C. Canadensis. Baird ! 

 v.s.p. Length of head and body variable, of a fully grown one, 

 generally 40 or 45 inches, of the tail 11 J- inches; fur dense, con- 

 sisting of an inner greyish black down and a longer coarse hair 

 of a chesnut colour more or less verging to black ; nose obtuse ; 

 eyes small; ears short, thick and rounded, and susceptible of clo- 

 sure at the will of the animal, by a verticle apposition of the au- 

 ricle ; toes, fore feet free ; of hind feet with large callous soles and the 

 toes palmated; the 2d toe with two nails, the inferior of which is 

 rounded with a cutting edge ; the inner toe has a less perfect double 

 nail, the rest have simple nails ; tail linguaform, with angular oval 

 soft scales, and hairs sparingly interspersed in their inte- 

 stices ; for a short distance from the body it is covered with 



hair. 



Genus Hystrix. 

 Gen. char. Incisors |, canines none, molars ^^ = 20. Molars 

 ■with flat tops, and a ridge of enamel ; head short and strong with 



Can. Nat. 5 Vol. VI. No. 4. 



