248 BULLETIN OF THE 



Each of the twenty-one species mentioned in the next table (Table 

 VI) has a comparatively restricted range, the western limit of their 

 habitats being in most cases the eastern border of the sterile plains of 

 the middle province. This list is composed principally of shrews, 

 moles, and rodents ; none of the first two groups and but a few of the 

 latter ranging across the continent. The absence of carnivores from 

 this list is its most striking feature. 



Table VII embraces fifteen species that, while restricted to America, 

 range from the Atlantic to the Pacific, and possess a correspondingly 

 wide distribution in latitude, most of them occurring nearly throughout 

 the northern continent. This list is composed almost exclusively of 

 carnivores and bats, all but one of the Massachusetts species of the 

 latter having been found in California, and at various intermediate 

 points. 



Table VIII contains thirteen species that are regarded in this paper as 

 common to the Old Word and the New ; ten of these are carnivores, 

 and include all the New England species of that group, except those 

 embraced in the preceding list. The geographical distribution of these 

 species, and of the groups to which they belong, affords further evi- 

 dence in favor of the supposition of the specific identity of their repre- 

 sentatives on the two continents above assumed ; each species rang- 

 ing as far north on both as it seems possible for mammalian life 

 to exist. Each has also an extended distribution southward, on each 

 continent, some of them ranging nearly or quite to the tropics ; which 

 shows them to be fitted to exist under widely varying physical condi- 

 tions. These conditions in the northern portions of their respective 

 habitats differ much more from those of the southern portions than those 

 of localities on the two continents ordinarily do when situated under 

 the same isotherm. The representatives of the species in question 

 from the eastern and western continents differ less, as has been previ- 

 ously stated, when the specimens compared are taken from those por- 

 tions nearly contiguous, as Northwestern America and Northeastern 

 Asia, than when they come from such widely distant points as East- 

 ern North America and Western Europe, the nearest affinity being 

 between those from the localities first mentioned, and the widest differ- 

 ences between those from the latter. The easternand western continents, 

 moreover, approach each other so nearly at Behring's Straits, that sev- 

 eral of the species in question are able to pass occasionally from one to 



