54 NATURAL SCIENCE. July, 



*' transition " zone is shown on the map, which in places attains a 

 breadth of over 300 miles, wherein the two faunas overlap. This 

 zone is mostly confined to the northern and mountain districts of the 

 United States, but it invades the British territories to the west of 

 Lake Winnipeg, to the north of Lakes Erie and Ontario, along the 

 southern bank of the St. Lawrence, and again in Nova Scotia. 



If we now examine the distribution of the seventy genera of 

 mammals given by Dr. Wallace as inhabiting the Nearctic Region, 

 we find that only eight Canis, Otaria, Bos, Sciurus, Scmroptenis, 

 Spermophihis, Hesperotnys, and Lepus can be fairly regarded as ranging 

 indiscriminately over the Boreal and Sonoran districts. Of these 

 only one, Hespevomys (the Vesper Mice), is peculiar to America, and, 

 on referring to Flower and Lydekker's " Mammalia," it appears that 

 this should be included in the Old World genus Cricetus. The Sea- 

 Lions (Otaria), though not Palaearctic, occur in other Old World 

 Regions. 



All other genera of North American mammals can be referred 

 to either the northern or Sonoran fauna, even though some of them 

 overstep the limits of the transition zone. 



The Boreal fauna of Dr.Merriam comprises thirty of Dr. AVallace's 

 general — Sorex, '■•Neosorex, Urotrichiis, '-'•'■ Condylura, Ursus, Lntva, 

 '■''Latax, Mustela, Gtdo, TrichecJms, PJioca, Cystophora, Cervus, Rangifer, 

 Alces, Ovis, ''-Haplocerus, '^'Ovihos, Taniias, Arctomys, Castor, •'•Haploodon, 

 Arvicola, Myodes, Cmiiculus, '■'■Phenacomys, ■■'•Fiber, -'Zapus, -''-Erethizon, and 

 Lagomys, of which only the ten marked by an asterisk are peculiarly 

 American. Of the remaining twenty, all but six : Ursus, Lntya, 

 Mustela, Cervus, Ovis, and Arvicola are only elsewhere to be found in 

 the Palaearctic Region, while, even of these six, Ursus, Ovis, and 

 Arvicola are characteristic northern genera, which can only be regarded 

 as incursors in the tropical regions where they occur. These facts 

 seem to point strongly to the affinity of the northern faunas of the Old 

 and New Worlds, and to require the union of Boreal American 

 with the Palaearctic Region of Sclater. It will be possibly urged as 

 an objection that Boreal America is admitted to be the home of ten 

 distinctively American genera. But if the relationships of these 

 be examined, it will be found that only two, Condylura and Erethizon, 

 are American in their affinities. The nearest relations of all the rest 

 must be sought in the Old World. And Condylura and Erethizon, 

 though confined to the Boreal Region, should be regarded as belonging 

 to the SonordiXi. fauna. 



If the genera of mammals already enumerated be compared with 

 Dr. Wallace's lists, it will be seen there are thirty-two remaining, 

 which are fairly reckoned by Dr. Merriam as distinctively Sonoran, 

 although nine of them range into the southern parts of the Boreal 

 division. Of these thirty-two, only five, Plecotus, Vesperugo, Vespertilio,. 



5 The genera adopted by Dr. Merriam are more favourable to his views than 

 those given by Dr. Wallace. I take, however, the latter as the basis for comparison. 



