324 GEOGRAPHICAL AWD GEOLOGICAL DISTRIBUTION. 



inhabits the waters of the Southern States from South Carolina to 

 Texas; and A. atrofuscus, the highland moccasin, found in the 

 mountain-region south of Virginia, and by many authors considered 

 to be only a variety of the last. The rattlesnakes proper are repre- 

 sented by some ten or more species, most of which are found in 

 the region of the Southwestern United States. Five species (or 

 varieties) are known east of the Mississippi, of which the common 

 or banded rattlesnake (C. horridus), which is still abundantly dis- 

 tributed between Texas and New England, has the most extended 

 range. The diamond - rattlesnake (C. adamanteus) inhabits the 

 Southern States. 



Although the greater number of species of North American non- 

 venomous Ophidia belong to genera or groups which are also largely 

 developed in, and are equally characteristic of, the Old World, as 

 Tropidonotus (Butaenia), Coluber (Bascanium), and Elaphis (Scoto- 

 phis), types but barely represented in the Neotropical realm — thus 

 clearly indicating the Old World affinities of the so-called " Nearc- 

 tic " fauna, it appears that all the species are distinct.* This is not 

 very surprising in view of the limited northern range, especially in 

 the Western Hemisphere,! of the majority of the species, which are 

 •incapable, and have been incapable for a long period past, of tra- 

 versing the chilled northern tracts by which at one time, dotibtless, 

 a union was effected between the two hemispheres. As a result of 

 this isolation new species have been formed. It is more remarkable 

 that the most northern of all ophidian genera, Viperus, the viper, 

 whose appearance on the American continent might have been con- 

 fidently looked for as a result of its extended range, is completely 

 wanting. Other anomalies of distribution are presented by the 

 distinctively American genera Heterodon and Dromicus, both of 

 which have representatives in the island of Madagascar, and the 

 family of pit-vipers (Crotalidse), which is largely developed in the 

 Oriental realm, but is wanting in Africa. 



Of the more important families of tropical and sub-tropical 



* By most American herpetologists EutEenia, Bascanium, and Sootophis 

 are considered to be distinct from the Old World genera with which they 

 have "been united by the greater number of European naturalists. 



t Several species are found in British Columbia along the Canadian bound- 

 ary-line, but it is doubtful whether any penetrate much beyond the fiftieth 

 parallel of latitude. 



