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274 



MONOGRAPnS OF NORTH AMERICAN RODENTIA. 



Under the head of each species will be found detailed measurements 

 r," many specimens collected at identical localities, which further siiow tlie 

 extent and character of the purely individual variations presented by the 

 different species. These tables show that the variation is not confined to 

 size, i)ut affects the relative size of the different parts of the body and skull. 

 Individual variation in the relative size of the ear, the feet, etc., to the general 

 size is also, in many cases, quite noteworthy, as will be fully noticed in con- 

 nection with the description of the species and varieties. The variation, 

 both in general size and the relative size of different parts, generally ranges 

 from 20 to upward of 30 per cent, of the average size, the difference between 

 the extremes being generally somewhat in proportion to the extent of the 

 series of examples compared. 



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III. OEOGEArillCAL DISTRIBUTION. 



The family Leporidte has representatives tliroughout the two American 

 continents, but is by far the most numerously represented in the temperate 

 parts of North America. A single species only {Lepus timidus) ranges to 

 the arctic coast, and is also circumpolar in its distribution, being found also 

 in the boreal parts of Asia and Europe. The American representatives of 

 tiiis species (forming variety arcticus) differ but slightly from their Old 

 World conspecific allies. In America, this species ranges over Greenland, 

 the Barren Grounds, Labrador, and portions of Newfoundland, to the south- 

 ward its habitat meeting, or slightly overlapping, that of L. a?nericaniis. 

 L. americanus extends from the Barren Grounds southward to about tlic 

 isotherm 52° Fahrenheit. Tliroughout most of this vast region, it forms 

 the sole representative of the family. To the southward, its iiabitat overlaps 

 the ranges of L, campestris and L. sijlvaticus. Toward the southern border 

 of its habitat, it runs into three recognizable varieties, differing, in their 

 extreme piiases of development, mainly in slight but pretty constant differ- 

 ences of color, yet they pass into each other by almost imperceptible grada- 

 tions. These varieties are turginianus, Bairdii, and Washingtoni. Variety 

 virginianus ranges over Southern New England and the more elevated parts 

 of the Middle States, souliiward to Virginia, and westward to Minnesota ; 

 variety Bairdii occupies the dry interior region of the northern portion of 

 the Rocky Mountain plateau ; while variety Washingtoni occura throughout 



