336 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



southern half is certainly closely allied. A portion of the Mexican high- 

 lands are undoubtedly to be included in the North Temperate Realm, 

 but their fauna is too little known to admit of the boundary being at 

 present definitely drawn. 



On the other hand, the lower portion of the Great Colorado Valley 

 and the coast region of Southern California are, perhaps, better refer- 

 able to the American Tropical Realm than to the North Temperate. At 

 the junction of the two realms, there must be a belt of debatable or 

 doubtful ground. The approximate boundary I would place near the 

 northern limit of distribution of such mammalian forms as Nasua, Dicotyles, 

 Manatus, Dasypus, and the tropical species of Felis (as, F. onca, F. par- 

 dalis, F. eyra, and F. yaguarundi). This boundary also coincides quite 

 nearly with the southern limit of distribution of the Lynxes, the Gray and 

 Prairie Wolves, the Common Fox, the Mink, the Black and Grizzly Bears, 

 the Wapati and Virginian Deer, the Bison, the Pronghorn, the Beaver, 

 Prairie Dogs, Muskrat, the Arvicolce, and the Moles (Scalops and Condy- 

 lura). Bassaris is properly tropical, although straggling considerably far- 

 ther northward than the other above-mentioned forms. Florida, for con- 

 venience, might be allowed to stand as a portion of the North Temperate 

 Realm, although, as I have previously shown, it forms a distinct fauna, 

 with strongly tropical affinities,* it having not less than twelve character- 

 istically tropical genera of birds, several tropical genera of mammals 

 (notably the Manatee and several Bats), and also several tropical genera 

 of Reptiles and Batrachians, none of which range much, if any, to the 

 northward of its southern half. 



The southern boundary of the North Temperate Realm in the Old 

 World may be doubtless approximately drawn near the same isotherm 

 (about the mean annuals of 68 to 70 F.). This coincides closely with 

 the southern boundary of the so-called Palsearctic Region. There is* 

 however, here a broader belt of debatable or transitional ground than 

 in the New World, into which so many tropical forms extend that it 

 becomes almost a question whether the boundary between Tropical and 

 Temperate life should not be carried considerably more to the northward, 

 so as to leave Mr. Wallace's " sub-regions" 2 and 4 (Mediterranean and 

 Manchurian) in the Tropical Realm rather than in the North Temperate. 

 Despite, however, the presence of a considerable number of tropical 

 genera in these regions, the North Temperate forms still greatly pre- 

 dominate. In the Western or " Mediterranean" district, for instance, we 

 have species of Macacus, one of which even reaches the Spanish Penin- 

 sula. Herpestes has a similar northward extension. Hyaena and Hystrix 

 range not only over most of this district, but also over the greater part 

 of the Manchurian, where we again find a species of Macacus, and meet 

 with Semnopithecus, while Hyrax just enters the Mediterranean from the 

 southward. On the western border of the Manchurian we get also Pte- 

 ropine Bats, and species of Equidce, straggling remnants of the more 



* Bull. Mus. Zoo!., vol. ii, pp. 301, 392. 



